tests/intel/kms_fbc_dirty_rect: cleanup the dirty rect tests

These tests rely on FBC is enabled, some FIFO underruns can
disable FBC and can trigger asserts. In case if such asserts
are triggered, we end up not clearing the used fbs and crcs.
Use  common functions to prepare and clear igt test parameters
as required for each tests

Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Reviewed-by: Santhosh Reddy Guddati <santhosh.reddy.guddati@intel.com>