scmi: smt: correct mmu_set_region_dcache_behaviour parameters

Since commit d877f8fd ("arm: provide a function for boards init code to
modify MMU virtual-physical map"), the mmu_set_region_dcache_behaviour_phys
parameters need to be aligned on MMU_SECTION_SIZE to avoid unpredictable
behavior (alignment was done previously done in the function
mmu_set_region_dcache_behaviour_phys).

CC: Etienne Carriere <etienne.carriere@linaro.org>
Fixes: 240720e9 ("firmware: scmi: mailbox/smt agent device")
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>