ARM: 8829/1: spinlock: use unified assembler language syntax

Convert the conditional infix to a postfix to make sure this inline
assembly is unified syntax. Since gcc assumes non-unified syntax
when emitting ARM instructions, make sure to define the syntax as
unified.

This allows to use LLVM's integrated assembler.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>