[nrf fromtree] soc: nordic: nrf54h: cpuapp: Don't use serial shell when ETR is used

ETR handler (for Coresight STM logging) is using console UART and
can act as the shell backend. When that happens default serial shell
backend shall be disabled (and it is by default enabled if there is
a zephyr,console chosen set.

Signed-off-by: Krzysztof Chruściński <[email protected]>
(cherry picked from commit 6253c06)

Author: nordic-krch

soc/nordic/nrf54h/Kconfig.defconfig.nrf54h20_cpuapp

@@ -11,4 +11,7 @@ config NUM_IRQS
 config NRF_REGTOOL_GENERATE_UICR
 	default y
 
+config SHELL_BACKEND_SERIAL
+	default n if NRF_ETR_SHELL
+
 endif # SOC_NRF54H20_CPUAPP || SOC_NRF54H20_ENGB_CPUAPP