Adds missing #include <linux/mm.h> drivers/tee/optee/smc_abi.c to fix
compile errors like:
drivers/tee/optee/smc_abi.c:405:15: error: implicit
declaration of function 'page_to_section'
[-Werror,-Wimplicit-function-declaration]
        optee_page = page_to_phys(*pages) +
                     ^
arch/arm/include/asm/memory.h:148:43: note: expanded from
macro 'page_to_phys'
                                               ^
include/asm-generic/memory_model.h:52:21: note: expanded
from macro 'page_to_pfn'
                    ^
include/asm-generic/memory_model.h:35:14: note: expanded
from macro '__page_to_pfn'
        int __sec = page_to_section(__pg);                      \
                    ^
drivers/tee/optee/smc_abi.c:405:15: note: did you mean
'__nr_to_section'?
arch/arm/include/asm/memory.h:148:43: note: expanded from
macro 'page_to_phys'
                                               ^
include/asm-generic/memory_model.h:52:21: note: expanded
from macro 'page_to_pfn'
                    ^
include/asm-generic/memory_model.h:35:14: note: expanded
from macro '__page_to_pfn'
        int __sec = page_to_section(__pg);                      \
                    ^
include/linux/mmzone.h:1365:35: note: '__nr_to_section'
declared here
static inline struct mem_section *__nr_to_section(unsigned long nr)

Fixes: c51a564a ("optee: isolate smc abi")
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Link: https://lore.kernel.org/r/20211021125539.3858495-1-jens.wiklander@linaro.org'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>