First, for building compel plugins, we already have
"-I compel/include/uapi" in ccflags and asflags, so there is
no need to add "-iquote include/uapi".

Second, let's refer to compel plugin uapi includes in a uniform way,
choosing the same way the external code does, i.e. #include <compel/...>.

Third, in a few cases simplify #include statements by including
compel/plugins/plugin-std.h instead of a number of plugins/std/*.h files.
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>