ARM: ux500: Cut down Kconfig options

These systems are not plentiful and do not have any
strict memory constraints. Cut down the configurability
and select what is needed for all of them so they simply boot,
keeping only the UX500_SOC_DB8500 symbol which is used
elsewhere in the kernel for now, but default it to y.

Cc: Loic Pallardy <loic.pallardy@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>