Fix arm64 sub-register definitions

The "value regs" field was filled incorrectly. It is supposed to list the
registers that *this* register is a sub-register of, not the other way around.
This manifested itself in "register read" showing only the smaller sub-registers
(and a bunch of tests not passing). I am not sure if the "invalidates" field is
correct either, but it's usage seems to be inconsistent, so I'll leave that as-is
for now.

llvm-svn: 284981