fix(bl1): invalidate SP in data cache during secure SMC

Invalidate the SP holding `smc_ctx_t` prior to enabling the data cache
when handling SMCs from the secure world. Enabling the data cache
without doing so results in dirty data either being evicted into main
memory, or being used directly from bl1. This corrupted data causes
system failure as the SMC handler attempts to use it.

Change-Id: I5b7225a6fdd1fcfe34ee054ca46dffea06b84b7d
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>

bl1/aarch32/bl1_exceptions.S

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2016-2022, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -118,6 +118,14 @@ func smc_handler
 	mov	r0, #DISABLE_DCACHE
 	bl	enable_mmu_svc_mon
 
+	/*
+	 * Invalidate `smc_ctx_t` in data cache to prevent dirty data being
+	 * used.
+	 */
+	mov	r0, r6
+	mov	r1, #SMC_CTX_SIZE
+	bl	inv_dcache_range
+
 	/* Enable the data cache. */
 	ldcopr	r9, SCTLR
 	orr	r9, r9, #SCTLR_C_BIT