Finally add fpic compilation option to produce relocatable code.
Note that this requires to define CONFIG_NEEDS_MANUAL_RELOC for all
board files, also relocation support still has some limitations
(e.g. a developer should care not to overwrite the executing code or
memset() with zeroes not yet relocated data on malloc init etc.),
which may be fixed while switching to PIE.
Due to short investigation the architecture code is not ready for PIE
linking, this will require some manipulations with .dyn* sections.
Signed-off-by: Vladimir Zapolskiy <firstname.lastname@example.org>