Fix the INT2 mode mask to not include the "TEST" flag. Furthermore
remove the not needed reversion of bits when parsing the INT2 modes.
Instead reverse the INT2_MODE defines to match the bit order from the
datasheet.

Additionally mention the flag names from the datasheet for the different
modes in the comments.
Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>