Update libreriscv/HDL_workflow with instructions how to build and

install power_instruction_analyzer (pia)

diff --git a/libreriscv b/libreriscv
index bd0f1cca8b46ff5647398d5e41a90bed8ea4c0b2..9fe303b064624df441a038f4853dd2954c506df7 160000 (submodule)
--- a/libreriscv
+++ b/libreriscv
@@ -1 +1 @@
-Subproject commit bd0f1cca8b46ff5647398d5e41a90bed8ea4c0b2
+Subproject commit 9fe303b064624df441a038f4853dd2954c506df7