drm/i915: relocate _VGA_MSR_WRITE register definition
Move _VGA_MSR_WRITE to intel_crt_regs.h. It's not necessarily the
optimal place for it, but hands down better than i915_reg.h.
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241213115111.335474-2-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>