grub_git: set COMPATIBLE_HOST_armv7ve to null

grub_git: set COMPATIBLE_HOST_armv7ve to null

When build nxp-ls10xx which enable hard-float, it try to force soft-float:
| checking if compiling with clang... no
| checking for options to compile assembly...
| checking whether -freg-struct-return works... yes
| checking for options to get soft-float... no
| configure: error: could not force soft-float

Set COMPATIBLE_HOST_armv7ve to null to skip the build.

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>