MAINTAINERS: Update stm32mp entry

Add mailing list for stm32mp architecture and board.
Signed-off-by: NPatrick Delaunay <patrick.delaunay@st.com>

MAINTAINERS

@@ -233,6 +233,7 @@ ARM STM STM32MP
 M:	Patrick Delaunay <patrick.delaunay@st.com>
 M:	Christophe Kerello <christophe.kerello@st.com>
 M:	Patrice Chotard <patrice.chotard@st.com>
+L:	uboot-stm32@st-md-mailman.stormreply.com (moderated for non-subscribers)
 S:	Maintained
 F:	arch/arm/mach-stm32mp
 F:	drivers/clk/clk_stm32mp1.c

board/st/stm32mp1/MAINTAINERS

 STM32MP1 BOARD
 M:	Patrick Delaunay <patrick.delaunay@st.com>
+L:	uboot-stm32@st-md-mailman.stormreply.com (moderated for non-subscribers)
 S:	Maintained
 F:	board/st/stm32mp1
 F:	include/configs/stm32mp1.h