Memory: replace PhysicalToVirtualAddress with a more dedicated function

There is no external use of PhysicalToVirtualAddress any more, so it there is no need to have a generic function that handles all physical regions. Also, the previous APT change makes it possible that linear heap has some regions mapped to old and new VAddr regions at the same time, so we need to check both region and mark cached for the mapped one. RasterizerMarkRegionCached would skip the unmapped one in its loop

src/core/memory.h

@@ -228,11 +228,6 @@ std::optional<PAddr> TryVirtualToPhysicalAddress(VAddr addr);
  */
 PAddr VirtualToPhysicalAddress(VAddr addr);
 
-/**
- * Undoes a mapping performed by VirtualToPhysicalAddress().
- */
-std::optional<VAddr> PhysicalToVirtualAddress(PAddr paddr);
-
 /**
  * Gets a pointer to the memory region beginning at the specified physical address.
  */