kselftest/arm64: Validate contents of EXTRA_CONTEXT blocks

kselftest/arm64: Validate contents of EXTRA_CONTEXT blocks

Currently in validate_reserved() we check the basic form and contents of
an EXTRA_CONTEXT block but do not actually validate anything inside the
data block it provides. Extend the validation to do so, when we get to the
terminator for the main data block reset and start walking the extra data
block instead.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220829160703.874492-8-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>