stm32mp1: update platform files to use MMC devices ...

Signed-off-by: Yann Gautier <yann.gautier@st.com>

tools: Make invocation of host compiler correct ...

HOSTCC should be used in any of the tools inside the tools/ directory
instead of CC. That way it is possible to override both values from the
command line when building the Trusted Firmware and the tools at the
same time. Also, use HOSTCCFLAGS instead of CFLAGS.

Also, instead of printing the strings CC and LD in the console during
the compilation of the tools, HOSTCC and HOSTLD have to be used for
clarity. This is how it is done in other projects like U-Boot or Linux.

Change-Id: Icd6f74c31eb74cdd1c353583399ab19e173e293e
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

tools: Fix broken object compilation rules ...

As these rules depend on non-existing headers as well (likely copy &
pasted from fiptool), they never matched, and the built-in rules were
used. That led to random breakages when e.g. CPPFLAGS was suddenly
evaluated and contained invalid options.

For the stm32image, this reveals that we were relying on the built-in
rules by passing -D_GNU_SOURCE via CPPFLAGS, rather than using CFLAGS as
used in the local rule. Fix that as well.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

tools: Add stm32image tool into TF-A ...

This tools adds a specific header to ST TF-A binary.
This header is used by STM32MP1 ROM code to check the bootloader.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Signed-off-by: Lionel Debieve <lionel.debieve@st.com>