greybus: sdio: fix defines for older kernels

Some of the options for mmc host, are not defined in older kernels.
MMC_CAP2_HS400_1_2V, MMC_CAP2_HS400_1_8V, MMC_TIMING_MMC_DDR52 and
MMC_TIMING_MMC_HS400.

To not use them for older versions.

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Tested-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>