Kernel: Add better support for bootloaders loading the kernel

Before I assumed that bootloaders loaded the kernel at physical address
0, but this patch kinda allows loading to different addresses. This
still doesn't fully work as kernel bootstrap paging relies on kernel
being loaded at 0

kernel/arch/x86_64/PageTable.cpp

@@ -1,6 +1,5 @@
-#include <kernel/Arch.h>
+#include <kernel/BootInfo.h>
 #include <kernel/CPUID.h>
-#include <kernel/InterruptController.h>
 #include <kernel/Lock/SpinLock.h>
 #include <kernel/Memory/kmalloc.h>
 #include <kernel/Memory/PageTable.h>
@@ -147,6 +146,18 @@ namespace Kernel
 		return (uint64_t*)page;
 	}
 
+	template<typename T>
+	static paddr_t V2P(const T vaddr)
+	{
+		return (vaddr_t)vaddr - KERNEL_OFFSET + g_boot_info.kernel_paddr;
+	}
+
+	template<typename T>
+	static vaddr_t P2V(const T paddr)
+	{
+		return (paddr_t)paddr - g_boot_info.kernel_paddr + KERNEL_OFFSET;
+	}
+
 	void PageTable::initialize_kernel()
 	{
 		ASSERT(s_global_pml4e == 0);