- split n_libdrm-drop-valgrind-dep.patch into
n_libdrm-drop-valgrind-dep-generic.patch and
n_libdrm-drop-valgrind-dep-intel.patch to fix build on s390 and
armv7l

- Only apply libdrm-drop-valgrind-dep.patch if valgrnid_support is
enabled (fix build on e.g. aarch64).

- renamed libdrm-drop-valgrind-dep.patch to
n_libdrm-drop-valgrind-dep.patch in order to mark it as 'never
to be upstreamed'

- Add libdrm-drop-valgrind-dep.patch (as source): drop dependency
on valgrind on generated pkgconfig files. The .pc files are
auto-generated by meson and are 'technically' correct, but we do
not want to inject valgrind here (we can get away with this hack
as it's only relevant when using pkg-config --static, and we
do not provide static libs anyway).