common/board_f.c: remove CONFIG_SYS_GENERIC_GLOBAL_DATA

CONFIG_SYS_GENERIC_GLOBAL_DATA is no longer used by any board or
platform, so support for it can be dropped.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Vladimir Zapolskiy <vz@mleia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>