OMAP2+: use global values for the SRAM PA addresses

The SRAM PA addresses are locally defined and used at
different places, i.e. SRAM management code and idle sleep code.

The macros are now defined at a centralized place, for
easier maintenance.

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

Signed-off-by: Jean Pihet <j-pihet@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>