gitlab: tweak comments in edk2/opensbi jobs

Get rid of comments stating the obvious and re-arrange remaining
comments. The opensbi split of rules for file matches is also
merged into one rule.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220629170638.520630-3-berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>