drivers: qcom: rpmh: disallow active requests in solver mode

Controllers may be in 'solver' state, where they could be in autonomous
mode executing low power modes for their hardware and as such are not
available for sending active votes. Device driver may notify RPMH API
that the controller is in solver mode and when in such mode, disallow
requests from platform drivers for state change using the RSC.

Change-Id: I6dccfabdf230d927b945b0bd1840233e69064c9d
Signed-off-by: Lina Iyer <ilina@codeaurora.org>
Signed-off-by: Raju P.L.S.S.S.N <rplsssn@codeaurora.org>