conf: omap-a15: fix the dtb file path for extlinux boot

The uboot extlinux is using kernel device tree variable to populate the
dtb files. The error occurs if the device tree files are in ti folder
since there is no ti folder in deploy directory. Fix the kernel device
tree path before using in the uboot extlinux.

Signed-off-by: Yogesh Siraswar <yogeshs@ti.com>

conf/machine/include/omap-a15.inc

@@ -19,13 +19,15 @@ UBOOT_ARCH = "arm"
 UBOOT_ENTRYPOINT = "0x80008000"
 UBOOT_LOADADDRESS = "0x80008000"
 
+DEVICETREE_FILE = "${@d.getVar('KERNEL_DEVICETREE').replace("ti/","")}"
+
 # Generate an extlinux.conf file
 UBOOT_EXTLINUX = "1"
 UBOOT_EXTLINUX_ROOT = "root=PARTUUID=${uuid}"
 UBOOT_EXTLINUX_BOOT_FILES = " \
     extlinux.conf;extlinux/extlinux.conf \
     ${KERNEL_IMAGETYPE} \
-    ${KERNEL_DEVICETREE} \
+    ${DEVICETREE_FILE} \
 "
 
 SPL_BINARY = "MLO"