ARM: ux500: remove u8500_secondary_startup from INIT section.

This patch removes u8500_secondary_startup from _INIT section, there are
two  reason for this removal.
1. discarding such a small code does not save much, given the RAM sizes.
2. Having this code discarded, creates corruption issue when we boot
smp-kernel with nr_cpus=1 or with single cpu node in DT.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>