ARM: dts: bcm283x: Fix pin function of JTAG pins

BCM2835 ARM Peripherals doc shows gpio pins 4, 5, 6, 12 and 13
carry altenate function, ALT5 for ARM JTAG

Fixes: 21ff8439 ("ARM: dts: bcm283x: Define standard pinctrl groups in the gpio node.")

Signed-off-by: Henry Zhang <henryzhang62@gmail.com>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Eric Anholt <eric@anholt.net>