binman: Add support for PowerPC mpc85xx 'bootpg + resetvec' entry

This entry contains the PowerPC mpc85xx boot page and resetvec
sections.

Signed-off-by: Jagdish Gediya <jagdish.gediya@nxp.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: York Sun <york.sun@nxp.com>