firmware: arm_sdei: Discover SDEI support via ACPI

firmware: arm_sdei: Discover SDEI support via ACPI

BugLink: http://bugs.launchpad.net/bugs/1756096
SDEI defines a new ACPI table to indicate the presence of the interface.
The conduit is discovered in the same way as PSCI.

For ACPI we need to create the platform device ourselves as SDEI doesn't
have an entry in the DSDT.

The SDEI platform device should be created after ACPI has been initialised
so that we can parse the table, but before GHES devices are created, which
may register SDE events if they use SDEI as their notification type.

Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit 677a60bd2003ff5517a0b502365112531446a3e3)
Signed-off-by: Manoj Iyer <manoj.iyer@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>