grub: Allow build on armv7ve/a with softfp

grub: Allow build on armv7ve/a with softfp

Grub tries to force the compilation in softfp mode for some known target
CPU. That is because it doesn't use floats or doubles and there are
known limitations of using a configuration with hardfp. There are though
target CPUs that grub won't know how to configure failing with something
similar to:

| checking for options to get soft-float... no
| configure: error: could not force soft-float

This change relaxes a bit the COMPATIBLE_HOST restriction to only apply
for hardfp configuration even for arm7ve/a.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>