pinctrl: bcm: Remove unused struct bcm6328_pingroup

After commit 0e3db163("pinctrl: bcm: Convert drivers to use struct pingroup
and PINCTRL_PINGROUP()"), no one use struct bcm6328_pingroup, so remove it.

Signed-off-by: Yuan Can <yuancan@huawei.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220927133926.103943-1-yuancan@huawei.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>