Toolchain: Patch QEMU to support reading kernel cmdline via RPI Mailbox

This commit backports my upstream QEMU patch to implement this
functionality, which is currently waiting for review.

It was submitted here:
https://lists.nongnu.org/archive/html/qemu-arm/2023-04/msg00549

Toolchain/BuildQemu.sh

@@ -37,13 +37,19 @@ pushd "$DIR/Tarballs"
         exit 1
     fi
 
-    if [ ! -d "$QEMU_VERSION" ]; then
-        echo "Extracting qemu..."
-        tar -xf "${QEMU_ARCHIVE}"
-    else
-        echo "Skipped extracting qemu"
+    # If the source directory exists, re-extract it again in case the patches have changed.
+    if [ -d "qemu-$QEMU_VERSION" ]; then
+        rm -rf "qemu-$QEMU_VERSION"
     fi
 
+    echo "Extracting qemu..."
+    tar -xf "${QEMU_ARCHIVE}"
+
+    pushd "qemu-$QEMU_VERSION"
+        for patch in "${DIR}"/Patches/qemu/*.patch; do
+            patch -p1 < "${patch}" > /dev/null
+        done
+    popd
 popd
 
 mkdir -p "$PREFIX"