common/board_f.c: change the macro name and remove it for PPC platforms

common/board_f.c: change the macro name and remove it for PPC platforms

For most PPC platforms, they will call the first get_clocks() in
init_sequence_f[] as they define CONFIG_PPC. CONFIG_SYS_FSL_CLK is
then defined to call the second get_clocks(), which should be
redundant for PPC.

Signed-off-by: Gong Qianyu <Qianyu.Gong@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>