thermal/int3400: export uuids

INT3400 currently supports only one policy, which can't be changed.
This change exports all available policies (uuids) to user space and
allow this to be changed.
It introduces an attribute group uuids in INT3400 platform driver.
There are two attributes exposed:
- available_uuids
- current_uuid

User space can set current_uuid via this interface to one of the
available uuids. The uuid change is communicated to firmware, only
when the current zone mode is changed to "enabled". So the ideal
sequence should be
- set INT3400 zone mode to "disabled"
- change current_uuid
- set INT3400 zone mode to "enabled"

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>