[aadwarf64] Add DWARF support for unwinding with FEAT_PAuth_LR enabled

[pratlucas]

This introduces DWARF support to enable unwinders to authenticate return addresses signed using FEAT_PAuth_LR, where the value of PC is used as an extra diversifier.

To achieve that, this proposes the following changes to the aadwarf64 document:

• Expanding usage of the RA_SIGN_STATE pseudo-register, allocating it's bit[1] to indicate wether the value of PC has been used for return address signing.
• Introducing a new vendor call frame instruction, DW_CFA_AARCH64_negate_ra_state_with_pc, which negates both bit[0] and bit[1] of RA_SIGN_STATE and instructs the unwinder to capture the current code location to be used when authenticating the return address.

Co-authored-by: Oliver Stannard oliver.stannard@arm.com

[pratlucas]

CC: @momchil-velikov , @DanielKristofKiss, @rearnsha