drm/i915: Store the /5 target clock in struct dpll on vlv/chv

Unify vlv/chv with earlier platforms so that the sturct dpll::dot
represents the /5 clock frequency (ie. DP symbol rate or HDMI
TMDS rate) rather than the *5 fast clock (/2 of the bitrate).
Makes life a little less confusing to get the same number back
in .dot which we fed into the DPLL algorithm.

v2: Actually just include the 5x in the final P divider
    Do the same change to the hand rolled gvt code
v3: Missed a few *5 in *_find_best_dpll()

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220309214301.22899-1-ville.syrjala@linux.intel.com