soc: nordic: move nrf_ironside from drivers/firmware to soc/nordic

Move the IronSide APIs to soc/nordic from drivers/firmware since
these are vendor specific APIs. The header files are now included
from <nrf_ironside/*.h>. Adjust code that uses these APIs accordingly.

Also move the DT binding for "nordic,ironside-call" from
bindings/firmware to bindings/misc.

Signed-off-by: Jonathan Nilsen <jonathan.nilsen@nordicsemi.no>