[nrf fromlist] soc: nordic: nrf54h: Disable GPD for MCUBoot

Disable GPD for MCUBoot build, as it cannot be
reinitialized later in application (SDFW does not
support reinitialization).

Also, remove the GPD disabling from the mcumgr sample
for nRF54H20 iron board app - it was the reinitialization
that caused problems.

Upstream PR #: 88958

Signed-off-by: Michal Kozikowski <[email protected]>
(cherry picked from commit bece1c22bbf04d417839635e482ecc9e45bd5c15)

Author: nordic-mik7

samples/subsys/mgmt/mcumgr/smp_svr/boards/nrf54h20dk_nrf54h20_cpuapp_iron.conf

@@ -6,6 +6,6 @@ config SOC_NRF54H20_GPD
 	imply NRFS
 	imply NRFS_GDPWR_SERVICE_ENABLED
 	select ONOFF
-	default y if SOC_NRF54H20_CPUAPP || SOC_NRF54H20_CPURAD
+	default y if !MCUBOOT && (SOC_NRF54H20_CPUAPP || SOC_NRF54H20_CPURAD)
 	help
 	  This option enables the Global Power Domain service.