smdk6410: remove keypad, my board does not have that

Signed-off-by: Fudong Bai <fudongbai@gmail.com>
smdk6410: remove lcd power part, as GPN(5) is used for gpio keys

Signed-off-by: Fudong Bai <fudongbai@gmail.com>
smdk6410: add gpio keys

keymap:
S2: KEY_LEFT
S3: KEY_RIGHT
S4: KEY_UP
S5: KEY_DOWN
S6: KEY_CALC
S7: KEY_ENTER

Signed-off-by: Fudong Bai <fudongbai@gmail.com>