PLAT-OMAP: MCBSP: Transform into platform driver

This patch transform mcbsp code into a very initial
implementation of a platform driver.

It also gets ride of ifdefs on mcbsp.c code.
To do it, a platform data structure was defined.

Platform devices are located in arch/arm/plat-omap/devices.c

Signed-off-by: Eduardo Valentin <eduardo.valentin@indt.org.br>
Signed-off-by: Tony Lindgren <tony@atomide.com>