ANDROID: Kconfig.gki: Add QCOM_SCM to QCOM Hidden configs

QCOM_SCM is needed to be able to boot on db845c and is normally
selected by modules such as QCOM_RMTFS_MEM.

This dependency got accidentally dropped before the holidays
when I moved the QCOM_RMTFS_MEM to a module instead of a gki
built in.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Bug: 146449535
Change-Id: Icf9b6fec1d45247ee67e50d6c13c6e410e3d8c12