[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:
f884b1cf
d1cbbd6b

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>

include/asm-arm/arch-iop13xx/uncompress.h

 #include <asm/types.h>
 #include <linux/serial_reg.h>
 #include <asm/hardware.h>
-#include <asm/processor.h>
 
 #define UART_BASE ((volatile u32 *)IOP13XX_UART1_PHYS)
 #define TX_DONE (UART_LSR_TEMT | UART_LSR_THRE)
@@ -9,7 +8,7 @@
 static inline void putc(char c)
 {
 	while ((UART_BASE[UART_LSR] & TX_DONE) != TX_DONE)
-		cpu_relax();
+		barrier();
 	UART_BASE[UART_TX] = c;
 }