Remove exit call and mayfail parameter from physmap_common().

The only call path where exit was reached was from physmap functions.

Callers of physmap() et al. which were not prepared to handle
ERROR_PTR return values have been adjusted.
physmap_try_ro() has been renamed to physmap_ro() and physmap_common()
slightly refactored due to the now removed *FAIL parameters.

Signed-off-by: Niklas Söderlund <niso@kth.se>
Signed-off-by: Stefan Tauner <stefan.tauner@student.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@student.tuwien.ac.at>

git-svn-id: svn://flashrom.org/flashrom/trunk@1745 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1