fix: plug memory map leak, save sp_el0, dynamic UART, kill loop

- Bootloader: reallocate memory map buffer when ExitBootServices fails,
  so GetMemoryMap doesn't scribble past the old allocation on retry.
- vectors.S: actually store sp_el0 into the exception frame. Previously
  it was read into x24 and then… vanished. EL0 tasks would wake up with
  a corrupted stack pointer. Not great.
- Serial: split hardcoded 0x09000000 into a fallback default; add
  SerialUpdate() so the DTB-parsed UART address actually gets used.
- DTB: add bounds check on reserved[] with PMM's 3 extra slots accounted
  for, so malformed/overstuffed DTBs don't silently corrupt memory.
- PMM.h: bump kVMMaxReservedRegions 128→256, define kPMMReservedRegionCount.
- Types.h: remove `#define loop while(1)`. while(true) is fine.
- Rename IOSerial* → Serial* — the IO prefix was redundant, Serial.c
  already lives under IO/.

Kernel/Include/VM/PMM.h

@@ -4,7 +4,8 @@
 enum {
     kVMPageSize = 4096,
     kVMBlocksPerByte = 8,
-    kVMMaxReservedRegions = 128,
+    kVMMaxReservedRegions = 256,
+    kPMMReservedRegionCount = 3,
 };
 
 typedef struct {
@@ -28,4 +29,4 @@ typedef struct {
 
 void PMMInitialize(VMBootMemoryMap* bootMap);
 Pointer PMMAllocatePage();
-void PMMFreePage(Address address);
+void PMMFreePage(Address address);