drm/i915/icl: Add TBT checks for PLL calculations

drm/i915/icl: Add TBT checks for PLL calculations

Add missing TBT check in the Pll calculation.

v2: do not use a auxiliary function to check if status is
TBT or not. (Paulo)

v3: Code style changes. (Paulo)

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1532648115-29795-1-git-send-email-anusha.srivatsa@intel.com