Put some code into the first 16K of flash

This basically shrinks the remaining size of flash in the portion
that goes after the internal flash drive.

Comparison of the overall flash usage:

BEFORE:

LINK build-PYBV10/firmware.elf
   text	   data	    bss	    dec	    hex	filename
 228412	    392	  28104	 256908	  3eb8c	build-PYBV10/firmware.elf

AFTER