configs: am335x_evm: Enable Fastboot

This config option was present in am335x_boneblack_defconfig, but we
have to use generic am335x_evm_defconfig now, as BBB defconfig was
removed in commit 8fa7f65dd02c ("configs: Remove
am335x_boneblack_defconfig"). So this patch merely brings that option
back.

Tested on BeagleBone Black:

    => fastboot 0
    $ fastboot flash rootfs rootfs.img

Fixes: 8fa7f65dd02c ("configs: Remove am335x_boneblack_defconfig")
Signed-off-by: Sam Protsenko <joe.skb7@gmail.com>
diff --git a/configs/am335x_evm_defconfig b/configs/am335x_evm_defconfig
index ddf47a0..66899c2 100644
--- a/configs/am335x_evm_defconfig
+++ b/configs/am335x_evm_defconfig
@@ -45,6 +45,9 @@
 CONFIG_DFU_NAND=y
 CONFIG_DFU_RAM=y
 CONFIG_USB_FUNCTION_FASTBOOT=y
+CONFIG_FASTBOOT_FLASH=y
+CONFIG_FASTBOOT_FLASH_MMC_DEV=1
+CONFIG_FASTBOOT_CMD_OEM_FORMAT=y
 CONFIG_DM_I2C=y
 CONFIG_MISC=y
 CONFIG_DM_MMC=y