Try to open the udmabuf dev node for the first time or return the
fd if the device was previously opened.

Based-on-patch-by: Gerd Hoffmann <kraxel@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Message-Id: <20210526231429.1045476-2-vivek.kasireddy@intel.com>

[ kraxel: fixup fcntl.h include ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>