Merge branch 'amd64-smp' of https://github.com/chyyuu/ucore_plus into mjj/amd64

This patch applies the difference between head of the two branches and
cleans up coding style issues.

Signed-off-by: Junjie Mao <eternal.n08@gmail.com>
Cleanup random build warnings

Signed-off-by: Junjie Mao <eternal.n08@gmail.com>