stm: Removed support for LTS kernel (4.9) EOL

The LTS 4.9 kernel version entered EOL in January 2023
for this reason it will no longer be supported and updated
in this repo.

Signed-off-by: mariotesi <mario.tesi@st.com>
Change-Id: I17fb2b26f9b6939190080322952d084060304018
Reviewed-on: https://gerrit.st.com/c/linuxandroidopen/stm-ldd-iio/+/324710
Tested-by: CITOOLS <MDG-smet-aci-reviews@list.st.com>
Reviewed-by: Matteo DAMENO <matteo.dameno@st.com>

README.md

@@ -1,5 +1,14 @@
 # Introduction
-This repository contains STMicroelectronics MEMS IIO drivers for Linux/Android kernels.
+This repository contains STMicroelectronics MEMS IIO drivers for the following LTS Linux/Android kernels:
+ - 4.9 (EOL)
+ - 4.14
+ - 4.19
+ - 5.4
+ - 5.10
+ - 5.15
+ - 6.1 (WIP)
+
+For EOL kernel the maintenance has been discontinued and is strongly discouraged from using it for new developments.
 
 ## Source code integration
 From your kernel source code directory add the git remote (i.e. stmems_iio_github) for this repository: