kernel/vm: Add sys_msync
kernel/vm: Add sys_msync

Our msync is mostly a dummy one and only handles MS_ASYNC,
which is a nop on most modern systems.

Signed-off-by: Pedro Falcato <d037c3eb54456eb57a351d3e1361e11b3d89c857@gmail.com>

heatd/Onyx,heatd/Onyx,heatd/Onyx,heatd/Onyx