MIPS: BCM63XX: remove bogus ENETSW_TXDMA interrupts from BCM6328

These were erroneously copied from BCM6368. BCM6328 does not expose the
ENETSW_TXDMA interrupts, and BCM_6328_HIGH_IRQ_BASE + 7 is actually used
for the second UART.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Patchwork: http://patchwork.linux-mips.org/patch/4090/
Signed-off-by: John Crispin <blogic@openwrt.org>