pinctrl: armada-37xx: Add comment for pcie1_reset pin group

Group name 'pcie1' is misleading as it controls only PCIe reset pin. Like
other PCIe groups it should have been called 'pcie1_reset'. But due to
backward compatibility it is not possible to change existing group name.
So just add comment describing this PCIe reset functionality.

Signed-off-by: Pali Rohár <pali@kernel.org>
Link: https://lore.kernel.org/r/20200724132457.7094-1-pali@kernel.org


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