msm: mdss: Increase IB/AB votes during cont splash screen

We now support high resolutions like 4K that need higher b/w votes.
Increase b/w vote to 2GBps for the duration of the continuous splash
screen logo.

Change-Id: I2c73e98ea769b252bee51d953d7cdc24f2b6668a
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>