[lldb][AArch64] Add thread local storage tpidr register

This register is used as the pointer to the current thread
local storage block and is read from NT_ARM_TLS on Linux.

Though tpidr will be present on all AArch64 Linux, I am soon
going to add a second register tpidr2 to this set.

tpidr is only present when SME is implemented, therefore the
NT_ARM_TLS set will change size. This is why I've added this
as a dynamic register set to save changes later.

Reviewed By: omjavaid

Differential Revision: https://reviews.llvm.org/D152516