drm/msm/dp: Split control register

Divide the DisplayPort controller's IO map into
sub modules as per hardware design. This avoids
unnecessary allocation of memory for the registers
which are not being used.

CRs-Fixed: 2113611
Change-Id: Iccd4e91a305f05ca6cb7daa33c52bcf9e0c1a3be
Signed-off-by: Samantha Tran <samtran@codeaurora.org>