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_4_defconfig b/configs/rpi_4_defconfig
index eac55cc..59472d7 100644
--- a/configs/rpi_4_defconfig
+++ b/configs/rpi_4_defconfig
@@ -29,6 +29,7 @@
 CONFIG_DFU_MMC=y
 CONFIG_SYS_DFU_DATA_BUF_SIZE=0x100000
 CONFIG_SYS_DFU_MAX_FILE_SIZE=0x200000
+CONFIG_BCM2835_GPIO=y
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_SDMA=y
 CONFIG_MMC_SDHCI_BCM2835=y