drm/msm/mdp5: Use updated MDP5 register names

Since MDSS registers were stuffed within the the MDP5 register
space, we had an __offset_MDP() macro to identify the offset
between the start of MDSS and MDP5 address spaces. This offset
macro expected a MDP index argument, which didn't make much
sense since we don't have multiple MDPs.

The offset is no longer needed now that we have devices for the 2
different register address spaces. Also, remove the "REG_MDP5_MDP_"
prefix to "REG_MDP5_".

Update the generated headers in mdp5.xml.h

We generally update headers as a separate patch, but we need to
do these together to prevent breaking build.

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>