arm: mach-k3: enable support for falcon mode

With CONFIG_SPL_OS_BOOT enabled, U-Boot checks for the return value of
spl_start_uboot to select between falcon or the regular boot flow. Where
a return value of 0 means 'boot to linux'.

This patch overrides the weak definition form common/spl/spl.c to allow
K3 devices to use falcon mode with SPL_OS_BOOT_SECURE enabled for the
A-Core SPL.

Signed-off-by: Anshul Dalal <anshuld@ti.com>

arch/arm/mach-k3/common.c

@@ -480,3 +480,11 @@ release_proc_ctrl:
 	proc_ops->proc_release(ti_sci, PROC_ID_MCU_R5FSS0_CORE1);
 	return ret;
 }
+
+#if IS_ENABLED(CONFIG_ARM64) && IS_ENABLED(CONFIG_SPL_OS_BOOT_SECURE)
+int spl_start_uboot(void)
+{
+	/* Always boot to linux on Cortex-A SPL with CONFIG_SPL_OS_BOOT set */
+	return 0;
+}
+#endif