Restructure i3100 Super I/O driver to match the rest of the codebase.

Restructure i3100 Super I/O driver to match the rest of the codebase.

 - i3100_early_serial.c:

    - Split out enter/exit functions as the other Super I/Os do.

    - Make i3100_enable_serial() take a device_t as usual, and convert
      it to use the standard pnp_* function instead of open-coding
      the same functionality by hand.

    - Factor out i3100_configure_uart_clk() from i3100_enable_serial(),
      we do the same in various other Super I/Os, e.g. ITE ones.

 - Add some #defines for register / bit values and some comments.

 - Only functional change: Don't set bit 1 of SIW_CONFIGURATION, it's
   marked as "READ ONLY, WRITES IGNORED" in the datasheet.

Signed-off-by: Uwe Hermann <uwe@hermann-uwe.de>
Acked-by: Peter Stuge <peter@stuge.se>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@6058 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1