arm: omap3: Compile clock.c with -marm option to unbreak OMAP3530

Boards with OMAP3530 SoC fail to boot since commit bd2c4522


("ti: armv7: enable EXT support in SPL (using ti_armv7_common.h)")
because it enabled the use of Thumb2 for the SPL.

Experiments have shown that the deadlock happens in the
prcm_init() function from 'arch/arm/mach-omap2/omap3/clock.c'.

This patch enforces the compilation of clock.c source file in
ARM mode and makes the deadlock disappear. We are yet to figure
out the root cause of the problem. Still this is somewhat
better than having non-bootable boards for years.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>