Becuase the board select menu in arch/arm/Kconfig is too big,
move the Davinci board select menu to davinci/Kconfig.

Move also common settings (CONFIG_SYS_CPU="arm926ejs" and
CONFIG_SYS_SOC="davinci").

Signed-off-by: Masahiro Yamada
Reviewed-by: Tom Rini
Cc: Heiko Schocher
Cc: Sandeep Paulraj