[NXP] Adding nxp_matter_support submodule

Adding a reference to the nxp_matter_support repo that would be used to get NXP SDK support files.

Signed-off-by: Gatien Chapon <gatien.chapon@nxp.com>

Author: chapongatien

.gitmodules

@@ -325,3 +325,8 @@
 	url = https://github.com/Infineon/optiga-trust-m.git
 	branch = matter_support
 	platforms = infineon
+[submodule "third_party/nxp/nxp_matter_support"]
+	path = third_party/nxp/nxp_matter_support
+	url = https://github.com/NXP/nxp_matter_support.git
+	branch = master
+	platforms = nxp