ARM: mx3+mx5: rename mxc_board_init to ${machine}_init

mxc_board_init is too generic to be useful.  Additionally change some
mxc_timer to ${machine}_timer, too.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>