Documentation: add DebugFS doc for HiSilicon SEC

Documentation: add DebugFS doc for HiSilicon SEC

BugLink: https://bugs.launchpad.net/bugs/1854549
This Documentation is for HiSilicon SEC DebugFS.

Signed-off-by: Longfang Liu <liulongfang@huawei.com>
Signed-off-by: Kai Ye <yekai13@huawei.com>
Reviewed-by: Zaibo Xu <xuzaibo@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
(cherry picked from commit cbfe56e6938b2f7ca5e78b04417ee07f7c8d87fb)
Signed-off-by: Ike Panhc <ike.pan@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>