sf: turn probe switch into a lookup table

This allows for arbitrarily long manufacturer ids following the JEDEC
standard of 0x7f continuation bytes.  It also makes adding new entries
easier as it's just one element in an array.  The downside is that it
increases code size a bit, but we're talking ~50 bytes.

Signed-off-by: Reinhard Meyer <u-boot@emk-elektronik.de>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>