egl/android: fix regression in drm_gralloc path (v2)

This patch fixes a regression in mesa 18.2 and mesa-dev branches
for HAVE_DRM_GRALLOC code path which is causing black screen on Android
and prevents boot due to SIGSEGV MAPERR crash related to unproper handling
of drm_gralloc drm FD in new droid_open_device() path.

Problem is due to c7bb8213 ("egl/android: Add DRM node probing and filtering")

To avoid the crash the former existing working droid_open_device() is restored,
renamed droid_open_device_drm_gralloc() and kept within HAVE_DRM_GRALLOC braces.

Tested with mesa-dev and mesa 18.2 branch and oreo-x86 bootanimation
and Androdi GUI booting is fixed with i965, nouveau, radeon.
The changes are compatible with gbm_gralloc, I've tested build with hwc too.

(v2) remove indentation from HAVE_DRM_GRALLOC pre-processor directive

NOTE: Definition of enum{} for GRALLOC_MODULE_PERFORM_GET_DRM_FD
is not necessary and it's actually causing a redefinition building error,
because in HAVE_DRM_GRALLOC path gralloc_drm.h is already exported
by libgralloc_drm which is currently still a dependency.

Fixes: c7bb8213 ("egl/android: Add DRM node probing and filtering")
Cc: "18.2" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Mauro Rossi <issor.oruam@gmail.com>
(cherry picked from commit 73b342c7)