Secure boot fails for load setup with pxeboot_setup.sh, as the kernel
signature check fails validation due to the recent grub2 update for
CVE-2020-15705. This commit updates pxeboot_setup.sh to use the older
stock grubx64.efi, which will postpone the kernel validation until the
load is installed.
Change-Id: Ic6bfd236b076fc9023a77b1c2d8b9d4f8feee8b8
Closes-Bug: 1933263
Signed-off-by: Don Penney <don.penney@windriver.com>