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

include/os/freebsd/spl/sys/simd_aarch64.h

@@ -45,6 +45,7 @@
 
 #include <sys/types.h>
 #include <machine/elf.h>
+#include <machine/md_var.h>
 
 #define	kfpu_allowed()		1
 #define	kfpu_initialize(tsk)	do {} while (0)

include/os/freebsd/spl/sys/simd_arm.h

@@ -44,6 +44,7 @@
 
 #include <sys/types.h>
 #include <machine/elf.h>
+#include <machine/md_var.h>
 
 #define	kfpu_allowed()		1
 #define	kfpu_initialize(tsk)	do {} while (0)

include/os/freebsd/spl/sys/simd_x86.h

@@ -45,6 +45,10 @@
 		fpu_kern_enter(curthread, NULL, FPU_KERN_NOCTX);\
 }
 
+#ifndef PCB_FPUNOSAVE
+#define	PCB_FPUNOSAVE	PCB_NPXNOSAVE
+#endif
+
 #define	kfpu_end()	{			\
 	if (__predict_false(curpcb->pcb_flags & PCB_FPUNOSAVE))	\
 		fpu_kern_leave(curthread, NULL);	\

include/os/freebsd/spl/sys/vnode.h

@@ -143,6 +143,10 @@ vn_flush_cached_data(vnode_t *vp, boolean_t sync)
 /*
  * Attributes of interest to the caller of setattr or getattr.
  */
+
+#undef AT_UID
+#undef AT_GID
+
 #define	AT_MODE		0x00002
 #define	AT_UID		0x00004
 #define	AT_GID		0x00008