dt-bindings: mmc: tegra: Add pinctrl for SDMMC drive strengths

Add pinctrls for 3V3 and 1V8 pad drive strength configuration for
Tegra210 sdmmc.

Tegra210 sdmmc has pad configuration registers in pinmux register
domain and handled thru pinctrl to pinmux device node.

Tegra186 and Tegra194 has pad configuration register with in the
SDMMC register domain itself and are handles thru drive strength
properties in sdmmc device node.

Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>