Module bootloader

Parse and split serial console options.

Documentation/kernel-parameters.txt says:
  ttyS<n>[,options]
            Use the specified serial port.  The options are of
            the form "bbbbpnf", where "bbbb" is the baud rate,
            "p" is parity ("n", "o", or "e"), "n" is number of
            bits, and "f" is flow control ("r" for RTS or
            omit it).  Default is "9600n8".
but note that everything after the baud rate is optional, so these are
all valid: 9600, 19200n, 38400n8, 9600e7r

Write bootloader configuration to disk.

When we get here, the bootloader will already have a default linux image. We only have to add images for the non-default kernels and adjust the default to reflect whatever the default variant is.