asdk-libdrm

libdrm: Add define for DRM_RDWR

mmap requires O_RDWR to be set if MAP_SHARED is requested
with PROT_WRITE. Adding DRM_RDWR (defined as O_RDWR) as a
valid flag that can be passed to DRM_IOCTL_PRIME_HANDLE_TO_FD
for buffers that need required mapping.

Signed-off-by: Hemant Hariyani <hemanthariyani@ti.com>