power: reset: msm: Allow configuring reset type via secure I/O

Some targets require that the Download Mode / EDL
configuration be performed by means of a Secure I/O write
to the TCSR_BOOT_MISC_DETECT register rather than through a
generic SCM operation. Provide a mechanism for specifying
the address of this register in the device tree, to use as
a fallback method if the generic SCM call to set the
download mode configuration is unavailable.

This is necessary to comply with atomicity requirements of the
secure environment.

Change-Id: I5d3fcb48b0b47815d4839a3b722b0462a1bca087
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>