Improve pixel-a.S Performance by Using SVE/SVE2

Imporve the performance of NEON functions of aarch64/pixel-a.S
by using the SVE/SVE2 instruction set. Below, the specific functions
are listed together with the improved performance results.

Command executed: ./checkasm8 --bench=ssd
Testbed: Alibaba g8y instance based on Yitian 710 CPU
Results:
ssd_4x4_c: 235
ssd_4x4_neon: 226
ssd_4x4_sve: 151
ssd_4x8_c: 409
ssd_4x8_neon: 363
ssd_4x8_sve: 201
ssd_4x16_c: 781
ssd_4x16_neon: 653
ssd_4x16_sve: 313
ssd_8x4_c: 402
ssd_8x4_neon: 192
ssd_8x4_sve: 192
ssd_8x8_c: 728
ssd_8x8_neon: 275
ssd_8x8_sve: 275

Command executed: ./checkasm10 --bench=ssd
Testbed: Alibaba g8y instance based on Yitian 710 CPU
Results:
ssd_4x4_c: 256
ssd_4x4_neon: 226
ssd_4x4_sve: 153
ssd_4x8_c: 460
ssd_4x8_neon: 369
ssd_4x8_sve: 215
ssd_4x16_c: 852
ssd_4x16_neon: 651
ssd_4x16_sve: 340

Command executed: ./checkasm8 --bench=ssd
Testbed: AWS Graviton3
Results:
ssd_4x4_c: 295
ssd_4x4_neon: 288
ssd_4x4_sve: 228
ssd_4x8_c: 454
ssd_4x8_neon: 431
ssd_4x8_sve: 294
ssd_4x16_c: 779
ssd_4x16_neon: 631
ssd_4x16_sve: 438
ssd_8x4_c: 463
ssd_8x4_neon: 247
ssd_8x4_sve: 246
ssd_8x8_c: 781
ssd_8x8_neon: 413
ssd_8x8_sve: 353

Command executed: ./checkasm10 --bench=ssd
Testbed: AWS Graviton3
Results:
ssd_4x4_c: 322
ssd_4x4_neon: 335
ssd_4x4_sve: 240
ssd_4x8_c: 522
ssd_4x8_neon: 448
ssd_4x8_sve: 294
ssd_4x16_c: 832
ssd_4x16_neon: 603
ssd_4x16_sve: 440

Command executed: ./checkasm8 --bench=sa8d
Testbed: Alibaba g8y instance based on Yitian 710 CPU
Results:
sa8d_8x8_c: 2103
sa8d_8x8_neon: 619
sa8d_8x8_sve: 617

Command executed: ./checkasm8 --bench=sa8d
Testbed: AWS Graviton3
Results:
sa8d_8x8_c: 2021
sa8d_8x8_neon: 597
sa8d_8x8_sve: 580

Command executed: ./checkasm8 --bench=var
Testbed: Alibaba g8y instance based on Yitian 710 CPU
Results:
var_8x8_c: 595
var_8x8_neon: 262
var_8x8_sve: 262
var_8x16_c: 1193
var_8x16_neon: 435
var_8x16_sve: 419

Command executed: ./checkasm8 --bench=var
Testbed: AWS Graviton3
Results:
var_8x8_c: 616
var_8x8_neon: 229
var_8x8_sve: 222
var_8x16_c: 1207
var_8x16_neon: 399
var_8x16_sve: 389

Command executed: ./checkasm8 --bench=hadamard_ac
Testbed: Alibaba g8y instance based on Yitian 710 CPU
Results:
hadamard_ac_8x8_c: 2330
hadamard_ac_8x8_neon: 635
hadamard_ac_8x8_sve: 635
hadamard_ac_8x16_c: 4500
hadamard_ac_8x16_neon: 1152
hadamard_ac_8x16_sve: 1151
hadamard_ac_16x8_c: 4499
hadamard_ac_16x8_neon: 1151
hadamard_ac_16x8_sve: 1150
hadamard_ac_16x16_c: 8812
hadamard_ac_16x16_neon: 2187
hadamard_ac_16x16_sve: 2186

Command executed: ./checkasm8 --bench=hadamard_ac
Testbed: AWS Graviton3
Results:
hadamard_ac_8x8_c: 2266
hadamard_ac_8x8_neon: 517
hadamard_ac_8x8_sve: 513
hadamard_ac_8x16_c: 4444
hadamard_ac_8x16_neon: 867
hadamard_ac_8x16_sve: 849
hadamard_ac_16x8_c: 4443
hadamard_ac_16x8_neon: 880
hadamard_ac_16x8_sve: 868
hadamard_ac_16x16_c: 8595
hadamard_ac_16x16_neon: 1656
hadamard_ac_16x16_sve: 1622