ARM: OMAP2+: fix gpmc_cs_remap: re-allocating chip-select address space based on DT

Each GPMC chip-select needs to be configured for (base-address,CS-size) so that
GPMC understands the address-space allocated to device connected externally.
These chip-select configurations (base-address, CS-size) follow some basic
mapping rules like:
- The CS size is programmable from 256 MBytes to 16 MBytes (must be a power of 2)
  and is defined by the mask field. Attached memory smaller than the programmed
  CS region size is accessed through the entire CS region (aliasing).
- The programmed 'base-address' must be aligned to the 'CS-size' boundary and
  be a power of 2.
- Valid CS-size values are {256MB(max), 128MB, 64MB, 32MB and 16MB (min)}
  Any intermediate values creates holes in the chip-select memory-map.

This patch adds above checks in gpmc_cs_remap() so that any invalid value
passed by DT <reg> property can be filtered before actually allocating the
address space.

Signed-off-by: Pekon Gupta <pekon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>