arm64: proton-pack: Expose whether the branchy loop k value

[ Upstream commit a1152be3 ]

Add a helper to expose the k value of the branchy loop. This is needed
by the BPF JIT to generate the mitigation sequence in BPF programs.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>