opcodes: aarch64: flags to denote subclasses of uncond branches

[Changes in V4]
  - Use F_SUBCLASS_OTHER for instructions where F_BRANCH_CALL or
    F_BRANCH_RET does not apply.
[End of changes in V4]

[No changes in V3]
[New in V2]

Use the two new subclass flags: F_BRANCH_CALL, F_BRANCH_RET, to indicate
call to and return from subroutine respectively.

opcodes/
	* aarch64-tbl.h: Use the new F_BRANCH_* flags.