meta-hpe: Update U-Boot from 2019.07 to 2020.10

Signed-off-by: Mike Garrett <mike.garrett@hpe.com>
Change-Id: I538f9e74fdc90d3eb1e7e778b2ff99777b0d07d7
diff --git a/meta-hpe/meta-gxp/conf/machine/include/gxp.inc b/meta-hpe/meta-gxp/conf/machine/include/gxp.inc
index 8f515d9..e318145 100644
--- a/meta-hpe/meta-gxp/conf/machine/include/gxp.inc
+++ b/meta-hpe/meta-gxp/conf/machine/include/gxp.inc
@@ -15,8 +15,8 @@
 DEFAULTTUNE ?= "armv6-novfp"
 require conf/machine/include/arm/arch-armv6.inc
 
-UBOOT_MACHINE = "gxp_defconfig"
-UBOOT_ENTRYPOINT = "0x40100000"
-UBOOT_LOADADDRESS = "0x40100000"
+UBOOT_MACHINE ?= "gxp_defconfig"
+UBOOT_ENTRYPOINT ?= "0x40100000"
+UBOOT_LOADADDRESS ?= "0x40100000"