drm/msm/sde: avoid disabling clks/bw when cont-splash is enabled

Avoid disabling the core clocks and bandwidth vote during
crtc disable when continuous splash screen is enabled as it
might result in flicker or underrun during the transition
from UEFI to kernel.

Change-Id: I9299918ada63bb51f490c1d1aa9e94d6d9249db3
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>