R-Car/Use-GPIO-for-SD-card-detection

Overview
R-Car boards use GPIO for SD card detection, not use built-in card detection pin, because we have some reasons:


 * Old Renesas SoCs don't have built-in card detection pin.
 * So, for consistency and reliability, we use GPIO for SD card detection on R-Car boards.
 * Using GPIO is an advantage for power management (clock gating and/or power domain) of SDHI modules.
 * If we use built-in card detection pin, we have to turn the SDHI module on anyway.

Remarks
The TMIO core supports built-in card detection by using the following commits.

c7cd630a9751 mmc: tmio: fix never-detected card insertion bug 497d1f965c20 mmc: tmio: support IP-builtin card detection logic