If you look in the altera_nios2 component then you will find, in the HAL directory, the header files which define alt_irq_enable_all and alt_irq_disable (try using find or windows "find in files" if you can't go to the right header file immediately).
This will explain what the context parameter is being used for, and will show you some examples of its use (within the alt_irq_enable function for example).
Is there a reason why you don't want to use a parameter? The functions usually optimise down to three instructions so I'm assuming space and speed aren't the reason.