remoteproc: qcom: Merge cleanup and fixup from the future

remoteproc: qcom: Merge cleanup and fixup from the future

This incorporates cleanups done in preparation for mainline submission;
halt regs comes from the tcsr syscon, the mdt loader uses
rproc_da_to_va() to simplify the api, supplies are handled, requesting
stop is implemented and a few minor cleanups of the DT binding.

Also included is a fix for an issue triggered by the latest DB410c
firmware, where using the mpss_region for verification of the mdt header
results in a timeout on verifying the rest of the modem firmware.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>