pinctrl: microchip-sgpio: lock RMW access

pinctrl: microchip-sgpio: lock RMW access

BugLink: https://bugs.launchpad.net/bugs/1969110
[ Upstream commit 7996c5f5ec7a20b3f6b8fae93fcf3cb8f1c01743 ]

Protect any RMW access to the registers by a spinlock.

Fixes: 7e5ea974e61c ("pinctrl: pinctrl-microchip-sgpio: Add pinctrl driver for Microsemi Serial GPIO")
Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20220226204507.2511633-2-michael@walle.cc
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 84940deb8dd35dc96385f8af3191dc91431b0831)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>