Prepare v2023.10-stm32mp-r3.1-rc3

Update version in Makefile to prepare the label v2023.10-stm32mp-r3.1
for OpenSTLinux V6.2.1

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Change-Id: Ie32ba3d7d76c7fb65856e0d77273c669cb9dce77

Author: Patrice Chotard

Makefile

@@ -3,7 +3,7 @@
 VERSION = 2023
 PATCHLEVEL = 10
 SUBLEVEL =
-EXTRAVERSION = -stm32mp-r3-rc7
+EXTRAVERSION = -stm32mp-r3.1-rc3
 NAME =
 
 # *DOCUMENTATION*