misc: rtsx: Check mmc support for RTS5261

This patch check mmc support when RTS5261 initialize,
and not support mmc default.

Signed-off-by: Rui Feng <rui_feng@realsil.com.cn>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/1604397298-2921-1-git-send-email-rui_feng@realsil.com.cn


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>