riscv: add to generate doc by arch [1/5]

PD#SWPL-131748

Problem:
new feature:add to generate doc by arch

Solution:
add docs source info to riscv dir

Verify:
N/A

Change-Id: Ic0d92f4afb157909764bd745ec5d5ceee35c8466
Signed-off-by: xiaohu.huang <xiaohu.huang@amlogic.com>
41 files changed