am43xx: Define common init stack pointer address in Kconfig

The init stack pointer was defined to the same value in each AM43xx
board defconfig. Move the common definition to the Kconfig option
declaration instead.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Reviewed-by: Tom Rini <trini@konsulko.com>
Tested-by: Derald D. Woods <woods.technical@gmail.com>
diff --git a/Kconfig b/Kconfig
index 45656e9..19ce371 100644
--- a/Kconfig
+++ b/Kconfig
@@ -236,7 +236,7 @@
 config HAS_CUSTOM_SYS_INIT_SP_ADDR
 	bool "Use a custom location for the initial stack pointer address"
 	depends on ARC || (ARM && !INIT_SP_RELATIVE) || MIPS || PPC || RISCV
-	default y if OMAP34XX || AM33XX
+	default y if OMAP34XX || AM33XX || AM43XX
 	default y if TFABOOT
 	help
 	  Typically, we use an initial stack pointer address that is calculated
@@ -252,6 +252,7 @@
 	depends on HAS_CUSTOM_SYS_INIT_SP_ADDR
 	default 0x4020ff00 if OMAP34XX
 	default 0x4030ff00 if AM33XX
+	default 0x4033ff00 if AM43XX
 	default TEXT_BASE if TFABOOT
 
 config SYS_MALLOC_F