rtio: workq: Select Early P4WQ threads init

Otherwise the RTIO Workqueue is not functional for devices during init.

An example of this issue is devices using SPI transfers with default
spi_rtio.

Signed-off-by: Luis Ubieda <luisf@croxel.com>
(cherry picked from commit 2ce2794)

subsys/rtio/Kconfig.workq

@@ -4,6 +4,7 @@
 config RTIO_WORKQ
 	bool "RTIO Work-queues service to process Sync operations"
 	select SCHED_DEADLINE
+	select P4WQ_INIT_STAGE_EARLY
 	select RTIO_CONSUME_SEM
 	help
 	  Enable RTIO Work-queues to allow processing synchronous operations