OMAP3: remove hardcoded values from the ASM sleep code

Using macros from existing include files for registers addresses.

Tested on N900 and Beagleboard with full RET and OFF modes,
using cpuidle and suspend.

Based on original patch from Vishwa.

Signed-off-by: Jean Pihet <j-pihet@ti.com>
Cc: Vishwanath BS <vishwanath.bs@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Tested-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>