boot/opensbi: move patches to 0.9/ subdir to only apply when the 0.9 version is selected

With the addition of support for custom opensbi version in commit
5c7166d387b (boot/opensbi: add support for version configuration), we can no
longer be sure that the Buildroot patches can be applied - So move them to a
0.9 subdir to ensure they are only applied when the _LATEST_VERSION is used.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>