arm64: Add __NR_* definitions for compat syscalls

This patch adds __NR_* definitions to asm/unistd32.h, moves the
__NR_compat_* definitions to asm/unistd.h and removes all the explicit
unistd32.h includes apart from the one building the compat syscall
table. The aim is to have the compat __NR_* definitions available but
without colliding with the native syscall definitions (required by
lib/compat_audit.c to avoid duplicating the audit header files between
native and compat).

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Conflicts:
	arch/arm64/include/asm/unistd32.h
	arch/arm64/kernel/kuser32.S

Change-Id: I8776881b5beb39769aadc4c4f14a51ea54325112