smb-lib: qpnp-smb2: cleanup parallel charging code

The parallel charging code has grown organically.
Clean up the following:
1. Use correct units for all unit based variables.
2. Use slave percent instead of master percent.
3. Remove parallel master module parameter.
4. Put PARALLEL_DISABLE where it belongs in battery psy.
5. Create a get_jeita_cc_delta function similar to get_step_cc_delta
   function.
6. Print errors when returning error codes.

Change-Id: I27ec29c3a6c5f3aac31705e60e1b8cf3270322a1
Signed-off-by: Nicholas Troast <ntroast@codeaurora.org>
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>