board: stm32mp1: add splash screen with stmicroelectronics logo

Display the STMicroelectronics logo with features VIDEO_LOGO and
SPLASH_SCREEN on STMicroelectronics boards.

With CONFIG_SYS_VENDOR = "st", the logo st.bmp is selected, loaded at the
address indicated by splashimage and centered with "splashpos=m,m".

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index bf851cf..523c17e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -633,6 +633,7 @@
 F:	include/dt-bindings/pinctrl/stm32-pinfunc.h
 F:	include/dt-bindings/reset/stm32mp*
 F:	include/stm32_rcc.h
+F:	tools/logos/st.bmp
 F:	tools/stm32image.c
 N:	stm
 N:	stm32