seccomp: Whitelist cacheflush since 2.2.0 not 2.2.3

seccomp: Whitelist cacheflush since 2.2.0 not 2.2.3

The cacheflush system call (found on MIPS and ARM) has been included in
the libseccomp header since 2.2.0, so include it back to that version.
Previously it was only enabled since 2.2.3 since that is when it was
enabled properly for ARM.

This will allow seccomp support to be enabled for MIPS back to
libseccomp 2.2.0.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Reviewed-By: Andrew Jones <drjones@redhat.com>
Acked-by: Eduardo Otubo <eduardo.otubo@profitbricks.com>