When PWM_Sysfs_Base constructor is called, global variable hal may not
have been initialized resulting in NULL dereferencing error.
Move hal dependent stuff from contructor to init method.
Sort include alphabetically and make them in order:
Main header
system headers
library headers
local headers
While reordering, change a include of endian.h to our sparse-endian.h
which is more reliant to toolchain changes.