drm/i915: Relocate icl_sanitize_encoder_pll_mapping()

Move icl_sanitize_encoder_pll_mapping() out from the middle
of the .{enable,disable}_clock() functions.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210205214634.19341-15-ville.syrjala@linux.intel.com