plat/arm/css/sgi: Fix bl32 receive event - 0xC4000061 issue
plat/arm/css/sgi: Fix bl32 receive event - 0xC4000061 issue

The issue is that, when interrupt is triggered and RAS handler
is entered, after interrupt handler finishes, TF-A will re-enter
bl32 and then crash.
sdei_dispatch_event() may return failing result in some cases,
for example kernel may not have registered a handler or RAS event
may happen early during boot. We restore the NS context when
sdei_dispatch_event() returns failing result.

error log :
Received delegated event
X0 :  0xC4000061
X1 :  0x0
X2 :  0x0
X3 :  0x0
Received event - 0xC4000061 on cpu 0
UnRecognized Event - 0xC4000061
Failed delegated event 0xC4000061, Status Invalid Parameter
Unhandled Exception in EL3.
x30            = 0x000000000401f700
x0             = 0xfffffffffffffffe
x1             = 0xfffffffffffffffe
x2             = 0x00000000600003c0

Signed-off-by: Ming Huang <df079edb5b7e0961d567ff23a97821008dfa76cf@linux.alibaba.com>
Change-Id: I9802e9a32eee0ac3b5a8bcc0362d0b0e3b71dc9f

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware