print memdebug to stderr

memory usage tracing outputs are debug info, so it should be moved to
stderr instead of stdout.

Signed-off-by: Dave Young <dyoung@redhat.com>
Improve documentation of rd.memdebug

Explain more about rd.memdebug verbose level in dracut.cmdline.7.asc.

Signed-off-by: Dave Young <dyoung@redhat.com>
Add memdebug at different points in 99base/init.sh

Previously I added several trace point to the begin of several
init hooks of systemd, old init script also need this debug info.

Doing same here as what's added in the systemd service scripts:
At cmdline hooks adding trace of "1+:mem 1+:iomem 3+:slab"
For other hooks adding trace of "1:shortmem 2+:mem 3+:slab"

Signed-off-by: Dave Young <dyoung@redhat.com>