msm/drm/sde: fix recursive clock enablement in sde_reg_dump

RSC mode state may call the sde_reg_dump to capture
the mode switch failure. This may lead to recursive
mdp clock enable sequence because rsc mode switch
might be called from same context.
This change adds a new debug_dump API which avoids
clock enable calls. Client can use this new API
if MDP clocks are already enabled.

Change-Id: I889bc8505f08ea60490c1c87fb74b918742ed14b
Signed-off-by: Lakshmi Narayana Kalavala <lkalaval@codeaurora.org>