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/configs/sifive_unmatched_defconfig b/configs/sifive_unmatched_defconfig
index c90b7bb..38b7acd 100644
--- a/configs/sifive_unmatched_defconfig
+++ b/configs/sifive_unmatched_defconfig
@@ -1,5 +1,5 @@
 CONFIG_RISCV=y
-CONFIG_SPL_GPIO_SUPPORT=y
+CONFIG_SPL_GPIO=y
 CONFIG_SYS_MALLOC_F_LEN=0x3000
 CONFIG_NR_DRAM_BANKS=1
 CONFIG_SPL_DM_SPI=y