This adds two functions:
void gpio_ll_switch_dir_output(gpio_port_t port, uword_t outputs);
void gpio_ll_switch_dir_input(gpio_port_t port, uword_t inputs);
The first configures GPIO pins specified by a bitmask as output, the
second configures the specified pins as input.
The main use case is to allow bit-banging bidirectional protocols using
more basic GPIO peripherals that do not implement open drain mode, such
as found e.g. on MSP430, ATmega, or SAM0.
It is not intended to implement this feature on modern MCUs with
sophisticated GPIO peripherals.
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