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/IO/Serial.h

@@ -2,8 +2,9 @@
 #include <Types.h>
 
 enum {
-    kUARTBaseAddress = 0x09000000, // TODO: make it dynamic by parsing DTB
+    kUARTBaseAddress = 0x09000000,
 };
 
-Int32 IOSerialPutCharacter(ASCII character);
-Int32 IOSerialPutString(const ASCII* string);
+void SerialUpdate(UInt64 address);
+Int32 SerialPutCharacter(ASCII character);
+Int32 SerialPutString(const ASCII* string);