Update OCC Make Process to use GPU Binaries

  - Update hostboot_binaries to point to latest commit containing
    occ gpu gpe binary
  - Add Config variables to conditionally compile occ using gpu
    gpe binary if enabled
  - Update OCC Makefile to use config vars
diff --git a/openpower/configs/witherspoon_defconfig b/openpower/configs/witherspoon_defconfig
index a7ef6be..44035fb 100644
--- a/openpower/configs/witherspoon_defconfig
+++ b/openpower/configs/witherspoon_defconfig
@@ -58,6 +58,8 @@
 BR2_PACKAGE_PETITBOOT=y
 BR2_PACKAGE_PETITBOOT_MTD=y
 BR2_OCC_BIN_FILENAME="occ.bin"
+BR2_OCC_GPU_BIN_FILENAME="gpu_gpe1.bin"
+BR2_OCC_GPU_BIN_BUILD=y
 BR2_CAPP_UCODE_BIN_FILENAME="cappucode.bin"
 BR2_PACKAGE_LOADKEYS=y
 BR2_IMA_CATALOG_DTS="POWER9"