Rename GPIO_SUPPORT to GPIO

Rename these options so that CONFIG_IS_ENABLED can be used with them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/README.SPL b/doc/README.SPL
index 3fa4314..c6c06f4 100644
--- a/doc/README.SPL
+++ b/doc/README.SPL
@@ -48,7 +48,7 @@
 CONFIG_SPL_LIBCOMMON_SUPPORT (common/libcommon.o)
 CONFIG_SPL_LIBDISK_SUPPORT (disk/libdisk.o)
 CONFIG_SPL_I2C_SUPPORT (drivers/i2c/libi2c.o)
-CONFIG_SPL_GPIO_SUPPORT (drivers/gpio/libgpio.o)
+CONFIG_SPL_GPIO (drivers/gpio/libgpio.o)
 CONFIG_SPL_MMC_SUPPORT (drivers/mmc/libmmc.o)
 CONFIG_SPL_SERIAL_SUPPORT (drivers/serial/libserial.o)
 CONFIG_SPL_SPI_FLASH_SUPPORT (drivers/mtd/spi/libspi_flash.o)