mmc: Change the frequency to MMC_HS_52 when selecting hs400

mmc: Change the frequency to MMC_HS_52 when selecting hs400

Per JESD84-B51 P47, host need to change frequency to <=52MHz
after setting HS_TIMING to 0x1, and host need to set the
8-bit DDR buswidth. Currently setting the frequency to 26MHz
and trying to switch 8-bit DDR buswidth resulting timeouts.

mmc dev 1 0
Select HS400 failed -110
switch to partitions #0, OK
mmc1(part 0) is current device

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>