grub2: bump up version

grub2: bump up version

After many years since the last release and a long time with grub 2.02
in beta, there is finally a release and it brings many bug fixes and
interesting features such as support for ARM.

Patch boot/grub2/0001-remove-gets.patch doesn't seem to be required
anymore as grub-core/gnulib/stdio.in.h has changed significantly since
"053cfcd Import new gnulib." and has another treatment for gets.
Patch
boot/grub2/0002-grub-core-gettext-gettext.c-main_context-secondary_c.patch
was a backport which is present after the bump and therefore is also no
longer necessary.

Since we're adding a Config.in comment, we also introduce a
BR2_TARGET_GRUB2_ARCH_SUPPORTS hidden boolean, in order to avoid
repeating the architecture dependencies.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
[Thomas: add BR2_TARGET_GRUB2_ARCH_SUPPORTS, remove bogus dependencies
on ARM and AArch64, since enabling Grub2 on those architectures is
done in another commit.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>