[9fans] LPAE patch for ARM

[Richard Miller <9fans@hamnavoe.com>]

There's a new patch bcm-lpae which uses the 64-bit page table format to
allow 32-bit ARM kernels to support more than 4GB of physical memory. At
present this is mainly of interest for the 8GB Raspberry Pi 4, but there's
nothing Pi-specific in the MMU code so it may have future application for
bigger ARM systems.

The LPAE page table format works on the Pi 2 and Pi 3 as well, where it
may provide a wee performance improvement from simpler page fault handling.
When building a bcm kernel, the choice of page descriptor format is determined
by putting either 'mmu' or 'mmu64' in the 'misc' section of the config file.

The patch has been applied in the current 9legacy SD card image for Raspberry Pi
on http://9legacy.org/download.html, and also in the 9pi SD card image on
http://9p.io/sources/contrib/miller (though nowadays for all practical purposes
I recommend 9legacy as a better choice). If you just want to update the kernel,
source is in http://9p.io/sources/contrib/miller/9/bcm as usual.


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