fix(stm32mp1): use dedicated folder for TBBR compilation

Compiling in the same folder as for non-TTBR case leads to that error:
arm-none-eabi-ld.bfd: build/stm32mp1-sdmmc/debug/bl2/bl2.elf
 section `xlat_table' will not fit in region `RAM'

Specify a dedicated directory for this compilation case.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I8f59069a4ab0313173711629c3bf0c9f9f884a2b
1 file changed