drm/xe: Move BAR definitions to dedicated file

We should keep all hardware definitions separated from the driver
code. Move LMEM_BAR definition to new regs/xe_bars.h file and also
add there GTTMMADR_BAR definition to avoid using magic 0 resource.

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/20240530133527.1328-3-michal.wajdeczko@intel.com