[MLAS] Fix building on FreeBSD / powerpc64le (#26895)
### Description
<!-- Describe your changes. -->
1. platform.cpp missed inclusion of sys/auxv.h (for elf_aux_info)
and machine/cpu.h (for PPC_FEATURE2_ARCH_3_00). I missed that in my
previous commit.
2. Same as on AIX, __vector int32_t is not defined and __vector int
needs to be used.
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
Fixes build on FreeBSD / powerpc64le platform.
