gralloc: list supported metadata types

Add function to get the metadata types supported by IMapper.
In future releases, we will add more standard types but upgrading
devices may not support those types. This function will allow the
framework to identify which metadata types the device supports.

Bug: 141632767
Test: VtsHalGraphicsMapperV4_0TargetTest

Change-Id: I760cf054d2b6f08a52ad70f4ae60a39a63500939