Finally retire cmd_confdefs.h and CONFIG_BOOTP_MASK!

All of the choices for CONFIG_BOOTP_ are now documented in
the README file.  You must now individually select exactly
the set that you want using a series of
    #define CONFIG_BOOTP_<x>
statements in the board port config files now.

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