[pauthabi64] Add note for RAARCH64_AUTH_GOT_ADD_LO12_NC

There is no equivalent for this relocation in the standard ABI
it is used by runtime code to calculate the address of
a GOT slot so it can be used as one of the inputs to an
authenticate instruction. Add a note that this matches up
with the :got_auth_lo12: operator for future reference.

Part of ARM-software#253

Author: smithp35

pauthabielf64/pauthabielf64.rst

@@ -1157,7 +1157,6 @@ The GOT entries must be relocated by AUTH variant dynamic relocations.
   |             |                                        |                                  | value to bits [11:0] of  |
   |             |                                        |                                  | X. No overflow check.    |
   +-------------+----------------------------------------+----------------------------------+--------------------------+
-
 .. raw:: pdf
 
    PageBreak
@@ -1171,7 +1170,9 @@ is the PAuth ABI equivalent of ``R_AARCH64_RELATIVE``. The underlying
 calculation performed by the dynamic linker is the same, the only
 difference is that the resulting pointer is signed. The dynamic linker
 reads the signing schema from the contents of the place of the dynamic
-relocation.
+relocation. The ``R_AARCH64_AUTH_GOT_ADD_LO12_NC`` relocation is an
+addition for the PAuth ABI and has no equivalent in (AAELF64_). It is
+used with the ``:got_auth_lo12:`` operator on an add instruction.
 
 .. table:: Additional AUTH Dynamic relocations