Revert "meson: Do not require libdrm for DRI2 on hurd"

This reverts commit 2fd85105c6.

Despite its name, egl_dri2 works under plain DRI without DRI2, and the
old autotools build system built it when $enable_dri = yes, with no
check for DRI2. A future commit will adapt meson.build to follow that
approach rather than this hackier one.

Note that the case removed in the second hunk is already dead code,
since system_has_kms_drm is false on GNU/Hurd, and could have been
dropped as part of 66d2ae0386 ("meson: forcefully disable libdrm when
host doesn't have it").

Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/587>
(cherry picked from commit 8461776a09)

.pick_status.json

@@ -294,7 +294,7 @@
         "description": "Revert \"meson: Do not require libdrm for DRI2 on hurd\"",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null,
         "notes": null

meson.build

@@ -562,7 +562,6 @@ if with_vulkan_icd_dir == ''
   with_vulkan_icd_dir = join_paths(get_option('datadir'), 'vulkan/icd.d')
 endif
 
-# GNU/Hurd includes egl_dri2, without drm.
 with_dri2 = (with_dri or with_any_vk) and (with_dri_platform == 'drm' or with_dri_platform == 'apple' or
   host_machine.system() == 'gnu')
 with_dri3 = get_option('dri3').disable_auto_if(not (system_has_kms_drm and with_dri2)).allowed()
@@ -1696,8 +1695,7 @@ with_gallium_drisw_kms = false
 if system_has_kms_drm
   dep_libdrm = dependency(
     'libdrm', version : '>=' + _drm_ver,
-    # GNU/Hurd includes egl_dri2, without drm.
-    required : (with_dri2 and host_machine.system() != 'gnu') or with_dri3
+    required : with_dri2 or with_dri3
   )
 else
   # We should prevent libdrm from being available when the target doesn't have it to avoid transitive