Convert CONFIG_SOC_DA8XX et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SOC_DA8XX
   CONFIG_SOC_DA850
   CONFIG_DA850_LOWLEVEL
   CONFIG_MACH_DAVINCI_DA850_EVM
   CONFIG_SYS_DA850_PLL_INIT
   CONFIG_SYS_DA850_DDR_INIT

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: David Lechner <david@lechnology.com>
[trini: Rework CONFIG_SYS_DA850_PLL_INIT so it's selected on SOC_DA8XX]
Signed-off-by: Tom Rini <trini@konsulko.com>