A few kernel and calling convention adjustments to make sigsend and
sigreturn work for arm.
. provide a arch_proc_setcontext for earm in kernel
. set LR in context of signal handler to provide a proper
return address (to __sigreturn)
. change __sigreturn to retrieve the sigcontext pointer
from the sigframe struct and pass it to _sigreturn() in r0
Change-Id: Icd135a70595382c79d11d8dd9876f6a6f1df41f8
e3e5cf6d34