firmware: qcom: scm: Convert SCM to platform driver

This patch converts the Qualcomm SCM firmware driver into a platform
driver.  It also adds clock management for firmware calls which require
clocks to be enabled during the duration of their execution.  Rate
setting of the core clock is also in place for higher performance.

Signed-off-by: Andy Gross <andy.gross@linaro.org>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>