power: qcom: Add support for FG software algorithms

Add fg-alg.c and fg-alg.h which can have the common software
features and algorithms that can be used by GEN4 FG driver and QG
driver later.

Change-Id: I5423b9e75c1d5eca9cbc4d9e1e229082f6007a94
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>