vp9_ethread: combine encoder counts in separate struct

Several frame counters in encoder are updated at SB level. Combine
those counters and put them in a separate struct, which allows us
to allocate one copy for each thread.

Change-Id: I00366296a13c0ada4d8fa12f5e07728388b6cab7
Code cleanup: remove unused members in RD_OPT

These 2 members in RD_OPT were moved to TileDataEnc struct
already, and therefore were removed here.

Change-Id: I22fee3b67f96e473a58e194a7edc76dbd48bfa04
Merge "vp9_ethread: combine encoder counts in separate struct"
Merge "Code cleanup: remove unused members in RD_OPT"