Add PPC cpu feature tests for FreeBSD and Linux

Add needed cpu feature tests for powerpc architecture.

Overview:
zfs_altivec_available() - needed by RAID-Z
zfs_vsx_available()     - needed by BLAKE3
zfs_isa207_available()  - needed by SHA2

Part 1 - Userspace
- use getauxval() for Linux and elf_aux_info() for FreeBSD
- direct including <sys/auxv.h> fails with double definitions
- so we self define the needed functions and definitions

Part 2 - Kernel space FreeBSD
- use exported cpu_features of <powerpc/cpu.h>

Part 3 - Kernel space Linux
- use cpu_has_feature() function of <asm/cpufeature.h>

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>
Closes #13725

include/os/freebsd/Makefile.am

@@ -50,6 +50,7 @@ noinst_HEADERS = \
 	%D%/spl/sys/sid.h \
 	%D%/spl/sys/sig.h \
 	%D%/spl/sys/simd.h \
+	%D%/spl/sys/simd_powerpc.h \
 	%D%/spl/sys/simd_x86.h \
 	%D%/spl/sys/spl_condvar.h \
 	%D%/spl/sys/string.h \