This change causes a performance regression on arm due to this PR
#300

src/arm/linux/aarch32-isa.c ====
152,153d151
< } else if (chipset->vendor == cpuinfo_arm_chipset_vendor_unknown) {
< cpuinfo_log_warning("VDOT instructions disabled: unknown chipset");

chipset->vendor is unknown on many, if not most new SoC, on all cpus, including qualcomm, google tensor, exynos.

The problem the code atttempts to address is some unisoc/mediatek soc using a faulty linux kernel that marks udot instructions as illegal on Cortex A55. sdot is okay. aarch64 udot is okay. As far as I know, sudot, usdot and i8mm are okay.
Other vendors either used a newer linux kernel, or patched the bug.

To avoid the issue, XNNPack doesnt use udot in either aarch32 or aarch64. But there is only 1 flag to detect both, and this isa->dot

Impact is a performance regression
On Samsung S23 qualcomm medium core (A720)
Was QS8MobileNetV2/real_time 10695 us
Now QS8MobileNetV2/process_time/real_time 32577 us

Samsung S23 Qualcomm
SoC name: Unknown
Microarchitectures:
1x Cortex-X3
4x Cortex-A715
3x Cortex-A510
Cores:
0: 1 processor (0), ARM Cortex-X3
1: 1 processor (1), ARM Cortex-A715
2: 1 processor (2), ARM Cortex-A715
3: 1 processor (3), ARM Cortex-A715
4: 1 processor (4), ARM Cortex-A715
5: 1 processor (5), ARM Cortex-A510
6: 1 processor (6), ARM Cortex-A510
7: 1 processor (7), ARM Cortex-A510

Samsung S22 Exynos
SoC name: Unknown
Microarchitectures:
1x Cortex-X2
3x Cortex-A710
4x Cortex-A510
Cores:
0: 1 processor (0), ARM Cortex-X2
1: 1 processor (1), ARM Cortex-A710
2: 1 processor (2), ARM Cortex-A710
3: 1 processor (3), ARM Cortex-A710
4: 1 processor (4), ARM Cortex-A510
5: 1 processor (5), ARM Cortex-A510
6: 1 processor (6), ARM Cortex-A510
7: 1 processor (7), ARM Cortex-A510