drm/xe: Move XEHP_MTCFG_ADDR register definition to xe_regs.h

We should not define registers directly in the code while we have
dedicated files for all register definitions. Move XEHP_MTCFG_ADDR
to regs/xe_regs.h

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240530133527.1328-2-michal.wajdeczko@intel.com