loader/arm/mmu: Set first available va to KERNEL_LOAD_BASE

* The existing code set the first available pa and va to
  the end of the page dirctory.
* The arm mmu code was attempting to identity map (va==pa)
  the memory, but also wanted memory to be in kernel space.
  This allocation method isn't possible on all boards
  (including the pi)
* We're adjusting the dynamic ram to KERNEL_LOAD_BASE
  plus the max size of the kernel. (which is what most
  other platforms are doing)

src/system/boot/arch/arm/arch_mmu.cpp

@@ -700,8 +700,8 @@ mmu_init(void)
 	sPageTableRegionEnd = (addr_t)sPageDirectory + 0x200000;
 
 	// Mark start for dynamic allocation
-	sNextPhysicalAddress =
-	sNextVirtualAddress = sPageTableRegionEnd;
+	sNextPhysicalAddress = sPageTableRegionEnd;
+	sNextVirtualAddress = KERNEL_LOAD_BASE + kMaxKernelSize;
 
 	// mark allocated ranges, so they don't get overwritten
 	insert_physical_allocated_range((addr_t)&_start, (addr_t)&_end - (addr_t)&_start);