serprog.c: Replace custom mapper with max_rom_decode

serprog's custom mapper is actually a hack to check for a maximum chip
size.  It would not have actually failed a read/write/erase attempt
since mappers are allowed to return NULL, it only printed a warning.

We can't remove custom mappers from SPI masters yet since some still
use it, but many of those are not actually needed or could be reworked,
so this is one step closer to removing SPI custom mappers.

Change-Id: If8b313708a52813b9354cbf45cb91cdd1fe36b13
Signed-off-by: Jonathon Hall <jonathon.hall@puri.sm>
---
M serprog.c
1 file changed, 28 insertions(+), 17 deletions(-)