Make retrieving SMPTE2094-10 metadata optional.

Devices that do not support this metadata are not required to support
getting or setting it on gralloc buffers, as SMPTE2094-10 is only used
for some HDR standards that are not guaranteed to be supported.

Bug: 205245993
Test: builds
Change-Id: Ic3501230015ddce49ce977963356c0578af7c50f