jtag: drivers: bcm2835gpio: don't allow GPIOs > 31

jtag: drivers: bcm2835gpio: don't allow GPIOs > 31

Current code assumes all the GPIO signals are manipulated via a single
32-bit register so using higher GPIOs silently fails.

Fix the check instead of trying to handle additional GPIOs (available on
Raspberry Pi Compute Modules) as that would slow the driver down.

Change-Id: Ib3b5864afb3b972d952f9b74665201cd93924959
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6658
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>