The current arasan sdhci PHY configuration isn't compatible
with the PHY on TI's AM654 devices.

Therefore, add a new compatible, AM654 specific quirks
and a new AM654 specific set_clock function which
configures the PHY in a sane way.
Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>