feat(st): add early console in BL2

Add an early UART console to ease debug before UART is fully configured.
This is done under flag STM32MP_EARLY_CONSOLE in the first STM32MP1
platform function called (bl2_el3_early_platform_setup()). It uses the
parameters defined for crash console: STM32MP_DEBUG_USART* macros.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: Id6be62368723a0499e97bbf56fb52c166fcbdfad
4 files changed