power: qcom: step-chg-jeita: Make read_range_data_from_node global

Currently, read_range_data_from_node() is used to read step
charging and SW JEITA thresholds from the battery profile. Since
this function can be shared with other drivers which only wants
to read the parameters but not use the entire step charging
algorithm, make read_range_data_from_node() a global function so
that it can be reused.

Also, maximum entries supported for step charging thresholds
should be made common.

Change-Id: If318cffba864aa1fd9a48f80d38134fb2fb69326
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>