Differentiate ultimate error messages depending on programmer used.

With every newly supported programmer the information regarding reboots
on failures becomes more ridiculous. With this patch it is only shown when
the internal programmer module was selected.

Example outputs for external programmers:
1) non-fatal:
[…]
Reading current flash chip contents... done. FAILED at 0x00000000! Expected=0xff, Found=0x28, failed byte count from 0x00000000-0x0001ffff: 0x1fde7
ERASE FAILED!
FAILED!
Uh oh. Erase/write failed. Checking if anything changed.
Good. It seems nothing was changed.
Writing to the flash chip apparently didn't do anything.
Please check the connections (especially those to write protection pins) between
the programmer and the flash chip. If you think the error is caused by flashrom
please report this on IRC at chat.freenode.net (channel #flashrom) or
mail flashrom@flashrom.org, thanks!

2) fatal:
[…]
Verifying flash... FAILED at 0x00000000! Expected=0x0f, Found=0xff, failed byte count from 0x00000000-0x0001ffff: 0x1fde6
Your flash chip is in an unknown state.
Please report this on IRC at chat.freenode.net (channel #flashrom) or
mail flashrom@flashrom.org, thanks!

Signed-off-by: Stefan Tauner <stefan.tauner@student.tuwien.ac.at>
Acked-by: David Hendricks <dhendrix@google.com>