Miscellaneous FreBSD compilation bugfixes

Add missing machine/md_var.h to spl/sys/simd_aarch64.h and
spl/sys/simd_arm.h

In spl/sys/simd_x86.h, PCB_FPUNOSAVE exists only on amd64, use PCB_NPXNOSAVE
on i386

In FreeBSD sys/elf_common.h redefines AT_UID and AT_GID on FreeBSD, we need
a hack in vnode.h similar to Linux. sys/simd.h needs to be included early.

In zfs_freebsd_copy_file_range() we pass a (size_t *)lenp to
zfs_clone_range() that expects a (uint64_t *)

Allow compiling armv6 world by limiting ARM macros in sha256_impl.c and
sha512_impl.c to __ARM_ARCH > 6

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Reviewed-by: Signed-off-by: WHR <msl0000023508@gmail.com>
Signed-off-by: Martin Matuska <mm@FreeBSD.org>
Closes #14674

module/zcommon/zfs_fletcher.c

@@ -136,8 +136,8 @@
 #include <sys/types.h>
 #include <sys/sysmacros.h>
 #include <sys/byteorder.h>
-#include <sys/spa.h>
 #include <sys/simd.h>
+#include <sys/spa.h>
 #include <sys/zio_checksum.h>
 #include <sys/zfs_context.h>
 #include <zfs_fletcher.h>

module/zcommon/zfs_prop.c

@@ -30,6 +30,10 @@
 
 /* Portions Copyright 2010 Robert Milkowski */
 
+#if defined(_KERNEL)
+#include <sys/simd.h>
+#endif
+
 #include <sys/zio.h>
 #include <sys/spa.h>
 #include <sys/u8_textprep.h>
@@ -1037,8 +1041,6 @@ zfs_prop_align_right(zfs_prop_t prop)
 
 #if defined(_KERNEL)
 
-#include <sys/simd.h>
-
 #if defined(HAVE_KERNEL_FPU_INTERNAL)
 uint8_t **zfs_kfpu_fpregs;
 EXPORT_SYMBOL(zfs_kfpu_fpregs);