fix(spmd): fix build error with spmd

Currently when we build with 'SPD=spmd SPMD_SPM_AT_SEL2=0'
options, this causes a build failure as
'plat_spmd_handle_group0_interrupt' is called irrespective of
'SPMD_SPM_AT_SEL2' usage in 'spmd_group0_interrupt_handler_nwd'

So make 'plat_spmd_handle_group0_interrupt' dummy implementation
available just when spmd is enabled and SPMC_AT_EL3 is disabled.

Change-Id: Iaccd38faab81671c98f9165f318145187dca9bc2
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/plat/arm/board/n1sdp/n1sdp_bl31_setup.c b/plat/arm/board/n1sdp/n1sdp_bl31_setup.c
index 6809541..bd05660 100644
--- a/plat/arm/board/n1sdp/n1sdp_bl31_setup.c
+++ b/plat/arm/board/n1sdp/n1sdp_bl31_setup.c
@@ -160,7 +160,7 @@
 		remote_dmc_ecc_setup(plat_info.remote_ddr_size);
 }
 
-#if defined(SPD_spmd)
+#if defined(SPD_spmd) && (SPMC_AT_EL3 == 0)
 /*
  * A dummy implementation of the platform handler for Group0 secure interrupt.
  */
@@ -169,4 +169,4 @@
 	(void)intid;
 	return -1;
 }
-#endif /*defined(SPD_spmd)*/
+#endif /*defined(SPD_spmd) && (SPMC_AT_EL3 == 0)*/