feat(bl32): enable r3 usage for boot args

`r3` is used to pass the base address of the transfer list. Make sure we
update the context structure with this register value so it is populated
with this information prior to executing the next stage.

Change-Id: Ie1eedbd2eb68b592df30779625691e8975d987bf
Signed-off-by: Harrison Mutai <[email protected]>

Author: harrisonmutai-arm

Diff for: bl32/sp_min/sp_min_main.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2024, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2016-2025, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -113,6 +113,7 @@ static void copy_cpu_ctx_to_smc_stx(const regs_t *cpu_reg_ctx,
 	next_smc_ctx->r0 = read_ctx_reg(cpu_reg_ctx, CTX_GPREG_R0);
 	next_smc_ctx->r1 = read_ctx_reg(cpu_reg_ctx, CTX_GPREG_R1);
 	next_smc_ctx->r2 = read_ctx_reg(cpu_reg_ctx, CTX_GPREG_R2);
+	next_smc_ctx->r3 = read_ctx_reg(cpu_reg_ctx, CTX_GPREG_R3);
 	next_smc_ctx->lr_mon = read_ctx_reg(cpu_reg_ctx, CTX_LR);
 	next_smc_ctx->spsr_mon = read_ctx_reg(cpu_reg_ctx, CTX_SPSR);
 	next_smc_ctx->scr = read_ctx_reg(cpu_reg_ctx, CTX_SCR);