arm64: capabilities: Group handling of features and errata workarounds

Now that the features and errata workarounds have the same
rules and flow, group the handling of the tables.

Reviewed-by: Dave Martin <dave.martin@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>