EmbeddedPkg/MmcDxe: Enable 4-bit mode even if SD_HIGH_SPEED is not supported

EmbeddedPkg/MmcDxe: Enable 4-bit mode even if SD_HIGH_SPEED is not supported

If SD doesn't support SD_HIGH_SPEED, function should still continue to
setup SD to go into 4 bits more if it is supported. Currently, the code
inadvertently exits early, but with a EFI_SUCCESS return code, and so
execution proceeds without ever attempting to enable 4-bit mode.

Since not having SD_HIGH_SPEED support is not an error, downgrade the
message that reports this to DEBUG_INFO.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Loh Tien Hock <tien.hock.loh@intel.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>