Modify existing class to create a PWM_Sysfs_Base class and derive it for
Bebop and Pwm_Sysfs (mainline kernel)
use asprintf for path allocation since it doesn't cost so much and is done
only at startup
Note that the constructor of the 2 classes : PWM_Sysfs and PWM_Sysfs_Bebop
allocate the paths and the constructor and desctuctor of class PWM_Sysfs_Base
frees them.
only keep in memory the paths that are needed later, i.e free _export_path,
_duty_path. The remaining path are freed in the destructor
This include some minor changes on all methods of PWM_Sysfs:
- Sort headers
- Add code inside Linux namespace rather than just use the namespace
- Declare a union pwm_params, that's only used to calculate at compile
time the maximum stack space we need in our methods: this is a bit
safer for future extensions
- Standardize error messages to include the useful params first and
then the error message
- Remove log message from hot path
- Don't abuse macros for checking error - convert the SNPRINTF_CHECK
macro into proper code, ignoring errors for not enough space since
they can't happen
- Fix call to read_file() passing uint8_t for "%u" in get_period()
- Fix passing char** instead of char* to write_file() in set_polarity()
- Use strncmp() instead of strncasecmp() since the kernel API uses
lowercase.
- Add comments on the 2 main methods of this class
