kernel: include modinfo for built-in modules

kernel: include modinfo for built-in modules

Add modules.builtin.modinfo to the kernel package, to support presence
testing using module aliases and printing module details with 'modinfo'.

With related kmodloader changes this adds ~2 KB to compressed image sizes.

     root@OpenWrt:/# modinfo unix
     name:           unix
     filename:       (builtin)
     alias:          net-pf-1
     license:        GPL

     root@OpenWrt:/# modprobe net-pf-1 && echo SUCCESS || echo FAIL
     SUCCESS

Signed-off-by: Tony Ambardar <itugrok@yahoo.com>