[ARM] pxa/tosa: move CONFIG_KEYBOARD_TOSA_USE_EXT_KEYCODES to mach/Kconfig

Tosa is now able to use generic matrix keypad driver instead of the deprecated
tosakbd.c, where CONFIG_KEYBOARD_TOSA_USE_EXT_KEYCODES is still useful.  Move
it to mach/Kconfig.

Signed-off-by: Eric Miao <eric.y.miao@gmail.com>