superio/nuvoton: Add support for NPCD378

superio/nuvoton: Add support for NPCD378

The NPCD378 can be found on at least:
* HP Compaq 8200
* HP Compaq 8300

The datasheet is not publicly available, as HP implements lots of
custom hardware. Add basic support for it, based on HP Compaq 8200.
The first eight LDNs seem to be standard nuvoton compatible, except for
LDN4, which is used to control front LED and power in ACPI S3.

LDN8 provides access to HP's proprietary HWM which is accessiable at the LDN's
IOBASE with a size of 0x100 bytes.
The HWM consists of 16 pages with each holding 0xff bytes. The pages can be
selected by writing the page index to IOBASE + 0xff.

TODO:
Reverse engineer the HWM to support fan control.

WARNING:
The remaining LDNs have been guessed and might be wrong!

The serial has been tested and is working.

Change-Id: Ib497fd41b88e9c159eeeffa69bc2bfdccee9cb38
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/25384
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>