target-i386: exception handling for memory helpers

This patch fixes exception handling for memory helpers
and removes obsolete PC update from translate.c.

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Pavel Dovgalyuk <pavel.dovgaluk@ispras.ru>
Signed-off-by: Richard Henderson <rth@twiddle.net>