stm32mp1: use unsigned values for SDMMC defines
stm32mp1: use unsigned values for SDMMC defines

Correct SDMMC macros to define unsigned values as expected by the
driver implementation.

Change-Id: Ib009f3df2cf26a9759d129eb571a27b2564770ce
Signed-off-by: Yann Gautier <e753f6969c288905606e3c07464886d4f1fc1be0@st.com>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware