misc: Use python f-strings for string formatting

This patch has been generated by applying flynt to the
gem5 repo (ext has been excluded)

JIRA: https://gem5.atlassian.net/browse/GEM5-831

Change-Id: I0935db6223d5426b99515959bde78e374cbadb04
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/68957
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>

configs/example/riscv/fs_linux.py

@@ -91,7 +91,7 @@ from common import Options
 
 
 def generateMemNode(state, mem_range):
-    node = FdtNode("memory@%x" % int(mem_range.start))
+    node = FdtNode(f"memory@{int(mem_range.start):x}")
     node.append(FdtPropertyStrings("device_type", ["memory"]))
     node.append(
         FdtPropertyWords(