ANDROID: add macros to create OEM data fields

Adds ANDROID_OEM_DATA and ANDROID_OEM_DATA_ARRAY macros
to add OEM-specific fields to kernel data structures
to enable value-added features implemented in vendor modules.
Fields defined with these macros must not be used by
SoC vendors who must use the ANDROID_VENDOR_DATA* macros
to add vendor fields.

Bug: 156285741
Signed-off-by: Todd Kjos <tkjos@google.com>
Change-Id: I93a8a182a17854cc4f0a86835e833bf9b00ea0b8