Currently, when the client attempts to do SDEI_EVENT_COMPLETE or
SDEI_EVENT_COMPLETE_AND_RESUME, the dispatcher pops off the outstanding
dispatch context for sanity check. There are however other checks
following this, which could potentially return failure. If that happens,
by popping the context, the dispatcher has inadvertently discarded a
valid context.

This patch fixes this bug by inspecting (not actually popping) the
outstanding context. The context is popped only after all error checks
are completed.

Change-Id: Ie199f6442f871a8177a8247a0c646543bad76d21
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

Change-Id: Ic381ab5d03ec68c7f6e8d357ac2e2cbf0cc6b2e8
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

This allows for other EL3 components to schedule an SDEI event dispatch
to Normal world upon the next ERET. The API usage constrains are set out
in the SDEI dispatcher documentation.

Documentation to follow.

Change-Id: Id534bae0fd85afc94523490098c81f85c4e8f019
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

The implementation currently supports only interrupt-based SDEI events,
and supports all interfaces as defined by SDEI specification version
1.0 [1].

Introduce the build option SDEI_SUPPORT to include SDEI dispatcher in
BL31.

Update user guide and porting guide. SDEI documentation to follow.

[1] http://infocenter.arm.com/help/topic/com.arm.doc.den0054a/ARM_DEN0054A_Software_Delegated_Exception_Interface.pdf

Change-Id: I758b733084e4ea3b27ac77d0259705565842241a
Co-authored-by: Yousuf A <yousuf.sait@arm.com>
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>