gdb: remove VALUE_NEXT_FRAME_ID, add value::next_frame_id

Remove VALUE_NEXT_FRAME_ID, replace it with a method on struct value.  Set
`m_location.reg.next_frame_id` directly from value::allocate_register_lazy,
which is fine because allocate_register_lazy is a static creation
function for struct value.

Change-Id: Ic9f0f239c166a88dccfee836f9f51871e67548e6
4 files changed