package/gobject-introspection: disable for riscv32

Fixes:
http://autobuild.buildroot.net/results/e32/e323f43952b3863cedfdae765b3fb10ec6b8d889/
http://autobuild.buildroot.net/results/53e/53e7b82baa9edb342cd110717d6b8ac82d5d933c/



And many more.

qemu-user 5.0.0 for riscv32 segfaults when running the g-i qemu wrapper, so
disable gobject-introspection.  There are no autobuilder failures for next,
so it looks to be fixed in qemu 5.1.0.

As python-gobject and gst1-python select gobject-introspection, add a
BR2_PACKAGE_GOBJECT_INTROSPECTION_ARCH_SUPPORTS symbol they can depend on
rather than having to propagate the dependencies.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>