slippy: Clean up for easier porting

Minor tweaks to variable names in the slippy mainboard
that make it easier to base a new board from without
as much renaming.

Also properly set up the thermal variables for the
thermal zone that is defined in ACPI instead of using
the generic setup from WTM2.

Change-Id: I752c1a50bfdc06b6ddad95bd1331c6870b9f9df2
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/56328
Reviewed-on: http://review.coreboot.org/4183
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
7 files changed