Fix build error with optimizations disabled (-O0)

Fix build error with optimizations disabled (-O0)

If Trusted Firmware is built with optimizations disabled (-O0), the
linker throws the following error:

    undefined reference to 'xxx'

Where 'xxx' is a raw inline function defined in a header file. The
reason is that, with optimizations disabled, GCC may decide to skip
the inlining. If that is the case, an external definition to the
compilation unit must be provided. Because no external definition
is present, the linker throws the error.

This patch fixes the problem by declaring the following inline
functions static, so the internal definition is used:

    inline void soc_css_security_setup(void)
    inline const arm_config_t *get_arm_config(void)

Change-Id: Id650d6be1b1396bdb48af1ac8a4c7900d212e95f