arm64: entry: Use SDEI event constants

Use SDEI_EV_FAILED instead of open coding the 1 to make it clearer how
SDEI_EVENT_COMPLETE vs. SDEI_EVENT_COMPLETE_AND_RESUME is selected.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20211118201811.2974922-1-f.fainelli@gmail.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>