add high pass filter support

[ladyada]

handy for slope mode!

[caternuson]

Works as far as basic get/set testing:

Adafruit CircuitPython 4.1.2 on 2019-12-18; Adafruit ItsyBitsy M4 Express with samd51g19
>>> import board
>>> from adafruit_lsm6ds import LSM6DS33, AccelHPF
>>> lsm = LSM6DS33(board.I2C())
>>> lsm.high_pass_filter_enabled
False
>>> lsm.high_pass_filter_enabled = True
>>> lsm.high_pass_filter_enabled
True
>>> lsm.high_pass_filter
0
>>> lsm.high_pass_filter = AccelHPF.SLOPE
>>> lsm.high_pass_filter
0
>>> lsm.high_pass_filter = AccelHPF.HPF_DIV100
>>> lsm.high_pass_filter
1
>>> lsm.high_pass_filter = AccelHPF.HPF_DIV9
>>> lsm.high_pass_filter
2
>>> lsm.high_pass_filter = AccelHPF.HPF_DIV400
>>> lsm.high_pass_filter
3
>>> lsm.high_pass_filter = 42
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/lib/adafruit_lsm6ds.py", line 386, in high_pass_filter
AttributeError: range must be an `AccelHPF`
>>> 

[ladyada]

thanks!