Move kernel to higher half.

Return to having the bootloader re-map the kernel into the higher
half before jumping into the kernel entrypoint, so we don't have
to juggle pointers inside the kernel.

src/boot/loader.h

@@ -8,6 +8,10 @@
 #define KERNEL_PHYS_ADDRESS 0x100000
 #endif
 
+#ifndef KERNEL_VIRT_ADDRESS
+#define KERNEL_VIRT_ADDRESS 0xFFFF800000000000
+#endif
+
 #ifndef VIRTUAL_OFFSET
 #define VIRTUAL_OFFSET 0xf00000000
 #endif
@@ -32,6 +36,10 @@
 #define KERNEL_LOG_PAGES 4
 #endif
 
+#ifndef KERNEL_PT_MEMTYPE
+#define KERNEL_PT_MEMTYPE 0x80000004
+#endif
+
 #ifndef KERNEL_FILENAME
 #define KERNEL_FILENAME L"kernel.bin"
 #endif