spi: bitbang: Replace spinlock by mutex

chipselect (in the case of spi-gpio: spi_gpio_chipselect, which
calls gpiod_set_raw_value_cansleep) can sleep, so we should not
hold a spinlock while calling it from spi_bitbang_setup.

This issue was introduced by this commit, which converted spi-gpio
to cansleep variants:
d9dda5a191 "spi: spi-gpio: Use 'cansleep' variants to access GPIO"

Replacing the lock variable by a mutex fixes the issue: This is
safe as all instances where the lock is used are called from
contexts that can sleep.

Finally, update spi-ppc4xx and and spi-s3c24xx to use mutex
functions, as they directly hold the lock for similar purpose.

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

include/linux/spi/spi_bitbang.h

@@ -4,7 +4,7 @@
 #include <linux/workqueue.h>
 
 struct spi_bitbang {
-	spinlock_t		lock;
+	struct mutex		lock;
 	u8			busy;
 	u8			use_dma;
 	u8			flags;		/* extra spi->mode support */