drm/xe: Fix conflicting intel_pcode_* symbols

drm/xe: Fix conflicting intel_pcode_* symbols

If CONFIG_DRM_XE_DISPLAY is set, the xe module can only be built as
module to avoid duplicate symbols from i915. The interface for pcode was
added without considering that, so the build breaks if both xe and i915
are built-in.

Since the intel_pcode_* functions should only be called from the display
side (xe side should call the xe interface directly) and there's already
a protection in Kconfig to avoid the problematic configuration, ifdef it
out in case CONFIG_DRM_XE_DISPLAY is disabled.

Closes: https://lore.kernel.org/r/3667a992-a24b-4e49-aab2-5ca73f2c0a56@infradead.org
Fixes: d9465cc8ac2d ("drm/xe/pcode: add struct drm_device based interface")
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/20250627-xe-kunit-v2-1-756fe5cd56cf@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>