fix(stm32mp2): add missing include

Without #include <plat/common/platform.h>, we have the following warning
with sparse:
plat/st/stm32mp2/bl2_plat_setup.c:15:6: warning: symbol
 'bl2_el3_early_platform_setup' was not declared. Should it be static?
plat/st/stm32mp2/bl2_plat_setup.c:23:6: warning: symbol
 'bl2_platform_setup' was not declared. Should it be static?
plat/st/stm32mp2/bl2_plat_setup.c:27:6: warning: symbol
 'bl2_el3_plat_arch_setup' was not declared. Should it be static?

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I18f9265c1eef1f8e8e0eac3d6c37a959e5c9e8b6
1 file changed