mpsl: Improve GRTC syscounter performance

Mandate NRF_GRTC_TIMER_AUTO_KEEP_ALIVE for platforms that have the GRTC.
This improves the worst case latency for reading the syscounter value.

NRF_GRTC_TIMER_AUTO_KEEP_ALIVE together with the grace period of the
GRTC should be sufficient to guarantee a low-latency for reading the
SYSCOUNTER where the latency actually matters.

This is needed to provide the performance that MPSL and the SoftDevice
controller expect. Without NRF_GRTC_TIMER_AUTO_KEEP_ALIVE it may take up
to around 100us to read the GRTC when it is in the inactive state.

Signed-off-by: Johan Stridkvist <[email protected]>

Author: jostn

mpsl/Kconfig

@@ -10,6 +10,7 @@ config MPSL
 	select IEEE802154_NRF5_EXT_IRQ_MGMT if IEEE802154_NRF5
 	select NRF_802154_MULTIPROTOCOL_SUPPORT if NRF_802154_RADIO_DRIVER
 	select MULTITHREADING_LOCK
+	select NRF_GRTC_TIMER_AUTO_KEEP_ALIVE if NRF_GRTC_TIMER
 	depends on (SOC_SERIES_BSIM_NRFXX || SOC_SERIES_NRF52X || SOC_NRF5340_CPUNET ||\
 			SOC_NRF54H20_CPURAD || SOC_SERIES_NRF54LX || SOC_SERIES_NRF71X)
 	help