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/Source/Arch/vectors.S

@@ -1,7 +1,7 @@
 .macro ventry type
     .align 7
     sub sp, sp, #288 // save 288 bytes of stack
-    stp x0, x1, [sp, #0] // move stack 
+    stp x0, x1, [sp, #0] // move stack
     mov x1, #\type // move type to x1
     b ExceptionsTrapEntry
 .endm
@@ -54,6 +54,7 @@ ExceptionsTrapEntry:
 
     stp x30, x21, [sp, #16 * 15]
     stp x22, x23, [sp, #16 * 16]
+    stp x24, xzr, [sp, #16 * 17]
 
     mov x0, sp
     bl ExceptionsHandler
@@ -92,4 +93,4 @@ ExceptionsVectorsInit:
     adr x0, ExceptionsVectorsTable
     msr vbar_el1, x0
     isb
-    ret
+    ret