pwm: Reorder symbols in core.c

This moves the functions called by pwm consumers above the functions
called by pwm providers. When character device support is added later
this is hooked into the chip registration functions. As the needed
callbacks are a kind of consumer and make use of the consumer functions,
having this order is more natural and prevents having to add
declarations for static functions.

Also move the global variables for pwm tables to the respective
functions to have them properly grouped.

Link: https://lore.kernel.org/r/eed83de07bdfb69b5ceba0b9aed757ee612dea8f.1706182805.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>