Current USDHC driver will reset VSELECT to 0 (3.3v) during mmc init,
then set to 1 for 1.8v eMMC I/O. When booting from eMMC, since ROM has
already set VSELECT to 1.8v before running the u-boot. This reset in
USDHC driver causes a short 2.2v pulse on CMD pin.

Fix this issue by not reset VSELECT to 0 when 1.8v flag is set.
Signed-off-by: Ye Li <ye.li@nxp.com>
(cherry picked from commit f01ebfda)