ARM: 7512/1: Fix XIP build due to PHYS_OFFSET definition moving

During the p2v changes, the PHYS_OFFSET #define moved into a
!__ASSEMBLY__ section. This causes a XIP build to fail with

 arch/arm/kernel/head.o: In function 'stext':
 arch/arm/kernel/head.S:146: undefined reference to 'PHYS_OFFSET'

Momentarily leave the #ifndef __ASSEMBLY__ section so we can
define PHYS_OFFSET for all compilation units.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>