xen/arm: cpufeature: Provide an helper to check if a capability is supported

xen/arm: cpufeature: Provide an helper to check if a capability is supported

The CPU capabilities will be set depending on the value found in the CPU
registers. This patch provides a generic to go through a set of capabilities
and find which one should be enabled.

The parameter "info" is used to display the kind of capability updated (e.g
workaround, feature...).

Signed-off-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>