[MTD] [NOR] Read extended device ID from AMD/Spansion CFI flash chips

AMD/Spansion use a device id of 0x7e to indicate an extended device is
present at offset 0xe and 0xf in the query data.

I've verified with Spansion that all their chips (mfr == 0x01) with an id
of 0x7e use it to indicate an extended id is present.  What's more, there
are no chips with a NON-extended id that is the same as a different chip's
extended id.  In other words, when the extended ID is present, one can
replace the normal id with the extended id without losing any information.
Which is what I've done.

Signed-off-by: Trent Piepho <tpiepho@freescale.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>