iommu: arm-smmu: Remove unused functions for qsmmuv500

These functions were originally added to do any one-time register
programming which requires halting/resuming the context bank. No such
register programming is required currently.

Additionally, this fixes an issue where the continuous splash screen
feature fails after the halt/resume sequence.

Change-Id: Ia55d80a322c8de4edd3e1a69f536340bd7c59812
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>