Convert CONFIG_BCM2835_GPIO to Kconfig

This converts the following to Kconfig:
   CONFIG_BCM2835_GPIO

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/rpi_0_w_defconfig b/configs/rpi_0_w_defconfig
index 8196182..a46c68d 100644
--- a/configs/rpi_0_w_defconfig
+++ b/configs/rpi_0_w_defconfig
@@ -24,6 +24,7 @@
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_TFTP_TSIZE=y
+CONFIG_BCM2835_GPIO=y
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_BCM2835=y
 CONFIG_DM_ETH=y