Fix OS_Memory 7 for discontiguous RAM
The current OS_Memory 7 implementation uses an address range structure returned by HAL_PhysInfo to decide which part of the physical address arrangement table to overwrite with RAM information. I suspect the original intention was for OS_Memory to use this address range to avoid marking the VRAM as DRAM (HAL_PhysInfo is expected to fill in the VRAM itself). But by overwriting everything between the start and the end address, OS_Memory will also overwrite any non-RAM areas which are sandwiched between RAM banks, e.g. the VideoCore-owned RAM on Pi models with >1GB RAM. There's also the problem that the address range returned by the HAL is using 32bit addresses, so it won't work as-is for RAM located above the 4GB barrier.
Fix these issues by reworking the routine so that it ignores the address range returned by the HAL and instead detects VRAM by checking the IsVRAM flag in the PhysRamTable entry. And for detecting if the ROM is running from RAM, instead of using the address range we can rely on the flag available via OS_ReadSysInfo 8 (i.e. HAL_PlatformInfo), like OS_Memory 8 does.
Also add a simple BASIC program (Dev.PhysInfo) to allow easy checking of HAL & OS physical address arrangement tables.