power: qpnp-fg: manually trim the external sense offset for bcl

Previous trim programs (TP_REV < 12) has a bug that causes the bcl
current readings to be off by up to 250 mA. Read the external sense
offset from the fuel gauge SRAM instead and use that if the TP_REV is
below 12.

Change-Id: Iac6344bdf429fece2126e1c521d47fc697efce02
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>