doc: bcm2835gpio: remove broken link and clarify usage

doc: bcm2835gpio: remove broken link and clarify usage

The peripheral address details have been removed from the documentation
part of the website (instead presented in the SoC datasheets).

Pi 5 GPIOs are provided by the RP1 southbridge, which requires the use
of libgpiod. The associated Linux driver for the GPIO interface must be
used when bitbashing on Pi 5, as the timing of pin state changes is not
guaranteed across the PCIe link without special treatment.

Using libgpiod, the typical maximum swclk speed is 1MHz.

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>
Change-Id: I8b2c44ec5edd71abaa0a763ba4d4f4603a211348
Reviewed-on: https://review.openocd.org/c/openocd/+/8884
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>