ARC: Fix signal frame management for SA_SIGINFO

Previously, when a signal was registered with SA_SIGINFO, parameters 2
and 3 of the signal handler were written to registers r1 and r2 before
the register set was saved. This led to corruption of these two
registers after returning from the signal handler (the wrong values were
restored).
With this patch, registers are now saved before any parameters are
passed, thus maintaining the processor state from before signal entry.

Signed-off-by: Christian Ruppert <christian.ruppert@abilis.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>