staging: fbtft: convert fbtft_reset() to be non-atomic

First of all, fbtft in current state doesn't allow to override GPIOs to be
optional, like "reset" one. It might be a bug somewhere, but rather out of
scope of this fix.

Second, not all GPIOs available on the board would be SoC based, some of them
might sit on I2C GPIO expanders, for example, on Intel Edison/Arduino, and thus
any communication with them might sleep.

Besides that using udelay() and mdelay() is kinda resource wasteful.

Summarize all of the above, convert fbtft_reset() function to non-atomic
variant by using gpio_set_value_cansleep(), usleep_range(), and msleep().

Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fbtft/fbtft-core.c

@@ -337,10 +337,10 @@ static void fbtft_reset(struct fbtft_par *par)
 	if (par->gpio.reset == -1)
 		return;
 	fbtft_par_dbg(DEBUG_RESET, par, "%s()\n", __func__);
-	gpio_set_value(par->gpio.reset, 0);
-	udelay(20);
-	gpio_set_value(par->gpio.reset, 1);
-	mdelay(120);
+	gpio_set_value_cansleep(par->gpio.reset, 0);
+	usleep_range(20, 40);
+	gpio_set_value_cansleep(par->gpio.reset, 1);
+	msleep(120);
 }
 
 static void fbtft_update_display(struct fbtft_par *par, unsigned int start_line,