uboot-imx

board: sama5d2_xplained: change SDHCI GCK's clock source to UPLL

Change the clock source of the SDHCI's generated clock from PLLA to
UPLL clock to align to Linux driver.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Andreas Bießmann <andreas@biessmann.org>