Initial long descriptor page table support
This set of changes adds initial support for the long descriptor page table format:
LongDescswitch in hdr.Options allows build-time selection of whether long or short descriptor page table format is used
- The HAL can now use RISCOS_AddRAM to register RAM above the 4GB barrier.
- The OS doesn't yet support the use of RAM above the 4GB barrier; any high RAM the HAL adds will be thrown away during RISCOS_Start. OS support for high RAM, along with other API extensions, will come in future merge requests.
- When the long descriptor format is in use, access privilege 1 (privileged read/write, user read-only) gets downgraded to be read/write for both privileged and unprivileged modes. This is due to the corresponding permissions not being supported by the long descriptor format. A proper fix for this is yet to be developed.
This is the minimal set of changes required to allow the BCM2835 & OMAP5 HAL changes to be merged.