serial@ add OMAP wakeup-enable register

Add the wakeup enable register to the list of OMAP-specific UART
registers.  This is to support forthcoming OMAP PM enhancements which
use the wakeup feature of the OMAP's 8250-based UART.

Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>