kvx: gas: missing aliases for $r14r15 in assembler.
Most registers from a register-pair suffixed by .lo and .hi suffixes.
This was not the case of $r14 and $r15 since they are defined by the
ABI: $r14 is the frame pointer, and $r15 is used to return aggregates
from functions. We do not add aliases for $r12 (the stack pointer) and
$r13 (the tls register).