mmc: sdhci-tegra: Add comment for PADCALIB and PAD_CONTROL NVQUIRKS

This patch adds comments about NVQUIRKS HAS_PADCALIB and NEEDS_PAD_CONTROL.

Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Link: https://lore.kernel.org/r/1591326240-28928-1-git-send-email-skomatineni@nvidia.com


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