drm/i915/ehl: Use an id of 4 while accessing DPLL4's CR0 and CR1

Although, DPLL4 enable and disable is associated with MGPLL1_ENABLE
register, we can use ICL_DPLL_CFGCR0/CR1 macros to access this dpll's
CR0 and CR1 registers by passing an id of 4 to these macros.

Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190717021316.18610-1-vivek.kasireddy@intel.com