devfreq: devfreq_spdm: Support scm and hvc

Currently SPDM driver uses hvc calls to support
the dcvs algorithm logic. On some targets this
dcvs algorithm support is present in TZ and which
is accessed via separate calls. Add SCM call to
support TZ based dcvs algorithm.

Change-Id: I197f0f13b4107047151e10e19e4849008607f3e8
Signed-off-by: Dan Sneddon <dsneddon@codeaurora.org>
Signed-off-by: Alok Chauhan <alokc@codeaurora.org>