[ARM] pxa: remove keypad register definitions from pxa-regs.h

Keypad registers are now fully defined within pxa27x-keypad.c, no
need to keep those definitions in pxa-regs.h

Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>