boards: imx943_evk: refine GIC and SCMI objects init priority

GIC ITS depends on kernel heap, so move GIC initialize to be behind of
heap which initialization priority is CONFIG_KERNEL_INIT_PRIORITY_OBJECTS
which is 30 by default.

MU mailbox and SCMI objects depend on GIC, so set their init priority
to be same with GIC, the initialization sequence decided by the dts
dependency although they use the same init priority.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>