sh: SuperH KEYSC platform driver

Add a platform driver for the SuperH KEYSC block.  The driver expects to get
mode, timing information and keypad layout from the board code as platform
data.  The board code is resonsible for pin configuration.

Both sh7343 and sh7722 should be supported, but only the sh7722 processor has
been tested so far.  SH_KEYSC_MODE_3 is yet to be tested.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Cc: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>