[ARM] pxafb: small cleanup of the smart panel code

Group smart panel related code in a more compact fasion, avoid abused
usage of #ifdef .. #endif.

Also fix the incorrect condition in pxafb_smart_init() to decide if it
is a smart panel or not. (should be '&' instead of '|')

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