u-boot-imx: Add version table

This table shows which BSP version used by each board.

Signed-off-by: Daiane Angolini <angolini@gmail.com>
u-boot-fslc: Add table for u-boot mainline

Signed-off-by: Daiane Angolini <angolini@gmail.com>
u-boot: Add uboot chapter

Signed-off-by: Daiane Angolini <angolini@gmail.com>
index: Add u-boot entry on index

Signed-off-by: Daiane Angolini <angolini@gmail.com>