MX25: tx25: Add _end section on nand_spl

Commit f326cbba (arm: fix incorrect monitor protection region in FLASH) missed to update
nand_spl/board/karo/tx25/u-boot.lds.

Add the _end section.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>

nand_spl/board/karo/tx25/u-boot.lds

@@ -63,6 +63,8 @@ SECTIONS
 		*(.dynsym)
 	}
 
+	_end = .;
+
 	.bss __rel_dyn_start (OVERLAY) : {
 		__bss_start = .;
 		*(.bss)