Since 00648d0282dcca1da453c0b20d27e24bf901a854, the correct serial console name
is ttySx instead of the older ttyOx. Reflect this in cmdline passed to kernel
via u-boot
[ci:skip-build]: already built successfully in CI
Resize the partition when using a pre-built image. We didn't notice that
this was missing, because N900 images are new and we only tested from
pmbootstrap install --sdcard, which already uses the full SD card size.
