Fix build issues:

mvrtc.c: In function 'rtc_get':
mvrtc.c:45: warning: implicit declaration of function 'readl'
mvrtc.c: In function 'rtc_set':
mvrtc.c:100: warning: implicit declaration of function 'writel'
dreamplug.c: In function 'board_early_init_f':
dreamplug.c:43: warning: implicit declaration of function 'kw_config_gpio'
dreamplug.c: In function 'board_init':
dreamplug.c:108: warning: implicit declaration of function 'kw_sdram_bar'
drivers/rtc/librtc.o: In function `rtc_set':
/home/ag/u-boot/u-boot-move-new-host/u-boot-video/drivers/rtc/mvrtc.c:92: undefined reference to `writel'
/home/ag/u-boot/u-boot-move-new-host/u-boot-video/drivers/rtc/mvrtc.c:103: undefined reference to `writel'
drivers/rtc/librtc.o: In function `rtc_reset':
/home/ag/u-boot/u-boot-move-new-host/u-boot-video/drivers/rtc/mvrtc.c:117: undefined reference to `readl'
/home/ag/u-boot/u-boot-move-new-host/u-boot-video/drivers/rtc/mvrtc.c:120: undefined reference to `readl'
drivers/rtc/librtc.o: In function `rtc_get':
/home/ag/u-boot/u-boot-move-new-host/u-boot-video/drivers/rtc/mvrtc.c:45: undefined reference to `readl'
/home/ag/u-boot/u-boot-move-new-host/u-boot-video/drivers/rtc/mvrtc.c:48: undefined reference to `readl'
...

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Jason Cooper <u-boot@lakedaemon.net>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Acked-by: Marek Vasut <marek.vasut@gmail.com>