mb/google/trulo: Register Firmware name for ISH

Define ISH main firmware name so ISH shim loader can load firmware
from file system.

BUG=b:354607924
TEST=Boot trulo board, check that ISH is enabled and loaded
lspci shows: 00:12.0 Serial controller: Intel Corporation Device 54fc

Change-Id: Id60cb416a1cce5407bd483f0ce54f477584459b1
Signed-off-by: Varun Upadhyay <varun.upadhyay@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83671
Reviewed-by: V Sowmya <v.sowmya@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Eric Lai <ericllai@google.com>

src/mainboard/google/brya/variants/baseboard/trulo/devicetree.cb

@@ -47,6 +47,7 @@ chip soc/intel/alderlake
 		device ref tcss_xhci on end
 		device ref ish on
 			chip drivers/intel/ish
+				register "firmware_name" = ""ish_fw.bin""
 				register "add_acpi_dma_property" = "true"
 				device generic 0 on end
 			end