FSL: Convert board/freescale/common/Makefile to use CONFIG_

Convert the board/freescale/common/Makefile to use
CONFIG_* options to select which files to conditionally
compile into the board/freescale/common library rather
than conditionally compiling entire files.

Now handles::
    CONFIG_FSL_PIXIS
    CONFIG_FSL_DIU_FB
    CONFIG_PQ_MDS_PIB

CONFIG_ID_EEPROM is introduced until CFG_ID_EEPROM is gone.

Signed-off-by: Jon Loeliger <jdl@freescale.com>