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/spl/sys/simd.h

@@ -26,13 +26,16 @@
  * $FreeBSD$
  */
 
-
 #ifndef _FREEBSD_SIMD_H
 #define	_FREEBSD_SIMD_H
+
 #if defined(__amd64__) || defined(__i386__)
 #include <sys/simd_x86.h>
-#else
 
+#elif defined(__powerpc__)
+#include <sys/simd_powerpc.h>
+
+#else
 #define	kfpu_allowed()		0
 #define	kfpu_initialize(tsk)	do {} while (0)
 #define	kfpu_begin()		do {} while (0)
@@ -40,4 +43,5 @@
 #define	kfpu_init()		(0)
 #define	kfpu_fini()		do {} while (0)
 #endif
+
 #endif