Convert CONFIG_CLOCK_SYNTHESIZER to Kconfig

This converts the following to Kconfig:
   CONFIG_CLOCK_SYNTHESIZER

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/am335x_boneblack_vboot_defconfig b/configs/am335x_boneblack_vboot_defconfig
index c255d17..3e12969 100644
--- a/configs/am335x_boneblack_vboot_defconfig
+++ b/configs/am335x_boneblack_vboot_defconfig
@@ -6,6 +6,7 @@
 CONFIG_TI_COMMON_CMD_OPTIONS=y
 CONFIG_DEFAULT_DEVICE_TREE="am335x-boneblack"
 CONFIG_AM33XX=y
+CONFIG_CLOCK_SYNTHESIZER=y
 CONFIG_SPL=y
 CONFIG_ENV_OFFSET_REDUND=0x280000
 CONFIG_DISTRO_DEFAULTS=y