drm/xe: Fix build without CONFIG_PM_SLEEP

Build without CONFIG_PM_SLEEP (such as for riscv) was failing due
to unused xe_pci_runtime_* functions.

Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>