meta-bletchley: update u-boot devicetree

Switch u-boot devicetree to ast2600-bletchley

This patch depend on the u-boot patch:
https://patchwork.ozlabs.org/project/openbmc/patch/20220211005419.14454-1-potin.lai@quantatw.com/

Signed-off-by: Potin Lai <potin.lai@quantatw.com>
Change-Id: Ia9c53f7c27b29cab6f12fdb4e0e10c05bb055a2e
diff --git a/meta-facebook/meta-bletchley/conf/machine/bletchley.conf b/meta-facebook/meta-bletchley/conf/machine/bletchley.conf
index 174d3c5..c0df356 100644
--- a/meta-facebook/meta-bletchley/conf/machine/bletchley.conf
+++ b/meta-facebook/meta-bletchley/conf/machine/bletchley.conf
@@ -2,7 +2,7 @@
 KERNEL_DEVICETREE = "${KMACHINE}-bmc-facebook-${MACHINE}.dtb"
 
 UBOOT_MACHINE = "ast2600_openbmc_spl_defconfig"
-UBOOT_DEVICETREE = "ast2600a1-evb"
+UBOOT_DEVICETREE = "ast2600-bletchley"
 SPL_BINARY = "spl/u-boot-spl.bin"
 SOCSEC_SIGN_ENABLE = "0"