ACPI: ibm-acpi: Implement direct-ec-access thermal reading modes for up to 16 sensors

This patch extends ibm-acpi to support reading thermal sensors directly
through ACPI EC register access.  It uses a DMI match to detect ThinkPads
with a new-style embedded controller, that are known to have forward-
compatible register maps and use 0x00 to fill in non-used registers and
export thermal sensors at EC offsets 0x78-7F and 0xC0-C7.

Direct ACPI EC register access is implemented for 8-sensor and 16-sensor
new-style ThinkPad controller firmwares as an experimental feature.  The
code does some limited sanity checks on the temperatures read through EC
access, and will default to the old ACPI TMP0-7 mode if anything is amiss.

Userspace ABI is not changed for 8 sensors, but /proc/acpi/ibm/thermal is
extended for 16 sensors if the firmware supports 16 sensors.

A documentation update is also provided.

The information about the ThinkPad register map was determined by studying
ibm-acpi "ecdump" output from various ThinkPad models, submitted by
subscribers of the linux-thinkpad mailinglist.  Futher information was
gathered from the DSDT tables, as they describe the EC register map in
recent ThinkPads.

DSDT source shows that TMP0-7 access and direct register access are
actually the same thing on these firmwares, but unfortunately IBM never
did update their DSDT EC register map to export TMP8-TMP15 for the second
range of sensors.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>

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