msm: bcl: Calculate current available using vbat and rbat

Remove the code that reads battery current and current now.
Read battery resistance from bms module. Use the equation
below to calculate the available current:
iavailable = vbatt - 3400 / rbatt

CRs-fixed: 488647
Change-Id: I7d7688cddad672155f9a3068583a47dd1bc5dff9
Signed-off-by: Archana Sathyakumar <asathyak@codeaurora.org>