As i915_pipe_output_combo_valid() is no more i915 specific, and
it supports both i915 & XE then rename the helper.

s/i915_pipe_output_combo_valid/intel_pipe_output_combo_valid/

V2, V3, V4: - Rebase

Signed-off-by: Bhanuprakash Modem <bhanuprakash.modem@intel.com>
Reviewed-by: Swati Sharma <swati2.sharma@intel.com>