[AVR] Rewrite the CBRRdK instruction as an alias of ANDIRdK

The CBR instruction is just an ANDI instruction with the immediate
complemented.

Because of this, prior to this change TableGen would warn due to a
decoding conflict.

This commit fixes the existing compilation warning:

  ===============
  [423/492] Building AVRGenDisassemblerTables.inc...
  Decoding Conflict:
                  0111............
                  01..............
                  ................
          ANDIRdK 0111____________
          CBRRdK 0111____________
  ================

After this commit, there are no more decoding conflicts in the AVR
backend's instruction definitions.

Thanks to Eli F for pointing me torward `t2_so_imm_not` as an example of
how to perform a complement in an instruction alias.

Fixes BugZilla PR38802.

llvm-svn: 351526