drivers: thermal: Add support to modify upper/lower limit and delay

Add support to modify the upper and lower limit for a thermal instance
and the polling and passive delay for a thermal zone using sysfs. This
will allow the userspace to dynamically tune the thermal zone's config.

Change-Id: I45adbbd2c95d59b9cec40472744253af0f2bc0fc
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>