omap: Fix omap-keypad by restoring old keypad.h without breaking omap2 boards that use matrix_keypad

Only mach-omap2 boards are currently using matrix_keypad. Allow
mach-omap1 boards to use the old style keypad.h without breaking.

Created against linux-2.6.32-rc5.
Compile tested with omap_3430sdp_defconfig and rx51_defconfig.
Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Tony Lindgren <tony@atomide.com>