gfx: drv: save pipe specific panel timing regs to an array

gfx: drv: save pipe specific panel timing regs to an array

We have the same set of panel timing regs for each pipe, so store them
to an appropriate array instead of separate variables named after the
pipe.

The CNTR, CONF, DPLL, PALETTE, MIPI registers are handled specially
during restore, so the parts related to those are cleaned up separately
in the upcoming patches.

The only functional change of this patch is that the CNTR register is
saved now before all the above generic registers, but as reading these
registers don't have a side-effect this shouldn't be a problem.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>