[lldb][AArch64] Correct top nibble setting in memory tag read tests

Due to a missing cast the << 60 always resulted in zero leaving
the top nibble empty. So we weren't actually testing that lldb
ignores those bits in addition to the tag bits.

Correct that and also set the top nibbles to ascending values
so that we can catch if lldb only removes one of the tag bits
and top nibble, but not both.

In future the tag manager will likely only remove the tag bits
and leave non-address bits to the ABI plugin but for now make
sure we're testing what we claim to implement.