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_evm_spiboot_defconfig b/configs/am335x_evm_spiboot_defconfig
index 50653ab..abcc3e6 100644
--- a/configs/am335x_evm_spiboot_defconfig
+++ b/configs/am335x_evm_spiboot_defconfig
@@ -6,6 +6,7 @@
 CONFIG_SPL_DM_SPI=y
 CONFIG_DEFAULT_DEVICE_TREE="am335x-evm"
 CONFIG_AM33XX=y
+CONFIG_CLOCK_SYNTHESIZER=y
 # CONFIG_SPL_MMC is not set
 CONFIG_SPL=y
 CONFIG_SPL_SPI_FLASH_SUPPORT=y