drm/i915: Rename intel_tc_phy_regs.h to intel_mg_phy_regs.h

An upcoming patch moves the DKL PHY register definitions to
intel_dkl_phy_regs.h, so for consistency rename intel_tc_phy_regs.h
containing only MG PHY register definitions to intel_mg_phy_regs.h.

Suggested-by: Jani Nikula <jani.nikula@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221025102644.2123988-3-imre.deak@intel.com