build: add 'quartus_options' backend option

Makes it possible to feed quartus custom options through a
'quartus_options' setting under [quartus] in the .system file.
The most useful use case is to feed quartus tools the '--64bit'
options, to avoid them from running out of mem as they would
when in 32-bit mode.
Merge branch 'for-openrisc' of https://github.com/skristiansson/orpsoc