Set shareability bit in page tables for IO region on Pi 2 onwards
RISCOS_MapInIO does relatively little processing on the L1PT flags that the HAL passes to it. However, when modules come along later and try to locate IO again, using OS_Memory 13, access permissions are specified using a variation on dynamic area flags. The kernel translates from these to L1PT flags, and one of the rules it applies is that the shareability bit is set if on a multiprocessor system. On Pi 2 and later, this means it doesn't find a match amongst the sections that were mapped in by the HAL, and in practice this means BCMVideo ends up causing 16MB of IO space to be mapped in twice.
Fix this by passing the L1_S flag to RISCOS_MapInIO on Pi 2 and later. This effectively frees up an additional 16MB of logical address space for dynamic areas.