drm/msm/sde: continuous splash support for multiple displays

This change extends continuous splash data structures to associate
splash resources in use for a particular display, and reads HW
registers to find connected hw blocks and associate it with
respective display splash data and handles per display resource
hand-off to client during first commit on respective display.
Boot-loaders can either share same splash memory and ramdump memory
or can program separate memory for each display. This change adds
required support for handling both options with ref-counting to
track splash memory usage by a display.

Change-Id: Idb9fdd6fe5f7c3d352bd206bcf4aacf6ad67803f
Signed-off-by: Prabhanjan Kandula <pkandula@codeaurora.org>