[ARM] 4494/1: iop13xx: fix up elf_hwcap compile breakage

[ARM] 4494/1: iop13xx: fix up elf_hwcap compile breakage

arch/arm/boot/compressed/misc.o: In function `valid_user_regs':
misc.c:(.text+0x74): undefined reference to `elf_hwcap'

This triggers after the various elf_hwcap cleanups in:
81979a01b5f4b9574ab1f232fbd4b7f6852342da
b9716e532648857ceb8fcea5ae36ff17ce1d2ce0

include/asm-arm/arch-iop13xx/uncompress.h calls cpu_relax while spinning on
a register value.  cpu_relax requires processor.h->ptrace.h->hwcap.h

'elf_hwcap' is defined as an extern, but since the uncompressor does not
link against arch/arm/kernel/setup.c 'elf_hwcap' remains undefined.

Fix is to open code the cpu_relax() call as barrier().

Cc: Lennert Buytenhek <kernel@wantstofly.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>