Fix incorrect way of acknowledging FIFO processing. Old code ORed old
value of register with index of FIFO buffer just processed, which
generated invalid value for acknowledge. This caused FIFO to repeatedly
returning same content. Both fdcan_receive() and fdcan_release_fifo were
affected.
Added some descriptions for missing parameters, (hopefully) clarified
some along the way. Fixed all can related warnings in doxygen logs.
Added doxgen tags where meaningful comments had been provided. Dropped
redundant comment separators.
Add stm32h7 support for FDCAN peripheral. Source level compatibility is
provided with stm32g4. Additional features of stm32h7 such as
configurable buffers are supported. Implementation offers feature parity
with stm32g4 implementation.
