Add shortcuts for chroots to the chroot command

Everytime I need to chroot into any of the non-native chroots I have to search through the wiki to find what value to use for the --suffix parameter. Since most of the time you want to enter the rootfs chroot for the current device or the buildroot for the current architecture. I think this can be made quicker by adding two arguments to the chroot command:

--rootfs: Enter the rootfs for the current device
--buildroot: Enter the foreign architecture build chroot (not sure about this name)