omap: McBSP: Introduce caching in register write operations

Determine cache size required per McBSP port at init time, based on
processor type running on.

Allocate space for storing cached copies of McBSP register values at
port request.

Modify omap_msbcp_write() function to update the cache with every
register write operation.

Modify omap_mcbsp_read() to support reading from cache or hardware.

Update MCBSP_READ() macro for modified omap_mcbsp_read() function API.

Introduce a new macro that reads from the cache.

Tested on OMAP1510 based Amstrad Delta using linux-omap for-next, commit
fb7380d70e041e4b3892f6b19dff7efb609d15a4 (2.6.33-rc3+ dated 2010-01-11).
Compile-tested with: omap_perseus2_730_defconfig, omap_generic_1610_defconfig,
omap_generic_2420_defconfig, omap_2430sdp_defconfig, omap_3430sdp_defconfig,
omap_4430sdp_defconfig with CONFIG_OMAP_MCBSP=y selected.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Acked-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Acked-by: Jarkko Nikula <jhnikula@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>