fix(fvp): add secure uart interrupt in device region

OP-TEE enables the use case of a secure interrupt triggered by the UART
driver. This interrupt is routed by FFA_INTERRUPT interface to OP-TEE.
Define the UART interrupt in the FF-A device region node.
Without this change, OPTEE panics at the boot with the following:

  |  I/TC: No non-secure external DT
  |  I/TC: manifest DT found
  |  I/TC: OP-TEE version: 4.3.0-23-gfcd8750677db
  |  I/TC: WARNING: This OP-TEE configuration might be insecure!
  |  I/TC: WARNING: Please check https://optee.readthedocs.io/en/latest/architecture/porting_guidelines.html
  |  I/TC: Primary CPU initializing
  |  E/TC:0 0 assertion '!res' failed at core/drivers/hfic.c:56 <hfic_op_enable>
  |  E/TC:0 0 Panic at core/kernel/assert.c:28 <_assert_break>
  |  E/TC:0 0 TEE load address @ 0x6284000

Change-Id: Icddcdfd032315aeee65ba3100f3a6b470a74435d
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

plat/arm/board/fvp/fdts/optee_sp_manifest.dts

@@ -46,6 +46,7 @@
 			base-address = <0x00000000 0x1c0a0000>;
 			pages-count = <1>;
 			attributes = <0x3>; /* read-write */
+			interrupts = <38 0x900>;
 		};
 	};
 };