Bug#994873: libdrm-dev: mssing dependency on valgrind

[Andre Heider <a.heider@gmail.com>]

I did some more digging and it looks like valgrind can just be disabled:
https://salsa.debian.org/xorg-team/lib/libdrm/-/blob/debian-unstable/meson.build#L256

And AFAICT it's only used for debugging purposes ("ioctl annotations"), 
on intel and freedreno:
$ git grep HAVE_VALGRIND
freedreno/freedreno_priv.h:#if HAVE_VALGRIND
intel/intel_bufmgr_gem.c:#if HAVE_VALGRIND
intel/intel_bufmgr_gem.c:#if HAVE_VALGRIND
intel/intel_bufmgr_gem.c:#if HAVE_VALGRIND

For comparison:

arch disables it:
https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=libdrm-git#n43

suse too (if I read that "%if 0%{?with_valgrind_support:1}" correctly):
https://build.opensuse.org/package/view_file/openSUSE:Factory/libdrm/libdrm.spec?expand=1

fedora enables it on supported arch (but has a valgrind-devel package)
https://src.fedoraproject.org/rpms/libdrm/blob/rawhide/f/libdrm.spec

I propose to:
- disable valgrind for now
- reenable it once there's a multiarch compatible valgrind-devel package
  See also https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=731228