Speed up memory page mapping (#2141)

- Memory::MapPages total samplecount was reduced from 4.6% to 1.06%.
- From main menu into the game from 1.03% to 0.35%

src/core/memory.cpp

@@ -71,16 +71,21 @@ static void MapPages(PageTable& page_table, VAddr base, u64 size, u8* memory, Pa
                                  FlushMode::FlushAndInvalidate);
 
     VAddr end = base + size;
-    while (base != end) {
-        ASSERT_MSG(base < page_table.pointers.size(), "out of range mapping at {:016X}", base);
+    ASSERT_MSG(end <= page_table.pointers.size(), "out of range mapping at {:016X}",
+               base + page_table.pointers.size());
 
-        page_table.attributes[base] = type;
+    std::fill(page_table.attributes.begin() + base, page_table.attributes.begin() + end, type);
+
+    if (memory == nullptr) {
+        std::fill(page_table.pointers.begin() + base, page_table.pointers.begin() + end, memory);
+    } else {
+        while (base != end) {
             page_table.pointers[base] = memory;
 
             base += 1;
-        if (memory != nullptr)
             memory += PAGE_SIZE;
         }
+    }
 }
 
 void MapMemoryRegion(PageTable& page_table, VAddr base, u64 size, u8* target) {