fconf: exclude fconf_dyn_cfg_getter.c from BL1_SOURCES

fconf: exclude fconf_dyn_cfg_getter.c from BL1_SOURCES

fconf_dyn_cfg_getter.c calls FCONF_REGISTER_POPULATOR(), which populates
the fconf_populator structure.

However, bl1/bl1.ld.S does not have:

        __FCONF_POPULATOR_START__ = .;
        KEEP(*(.fconf_populator))
        __FCONF_POPULATOR_END__ = .;

So, this is not linked to bl1.elf

We could change either bl1/bl1.lds.S or lib/fconf/fconf.mk to make
them consistent.

I chose to fix up fconf.mk to keep the current behavior.

This is a groundwork to factor out the common code from linker scripts.

Change-Id: I07b7ad4db4ec77b57acf1588fffd0b06306d7293
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>