nvmem: stm32: fix OPTEE dependency

nvmem: stm32: fix OPTEE dependency

The stm32 nvmem driver fails to link as built-in when OPTEE
is a loadable module:

aarch64-linux-ld: drivers/nvmem/stm32-bsec-optee-ta.o: in function `stm32_bsec:
stm32-bsec-optee-ta.c:(.text+0xc8): undefined reference to `tee_client_open_session'
aarch64-linux-ld: drivers/nvmem/stm32-bsec-optee-ta.o: in function `stm32_bsec:
stm32-bsec-optee-ta.c:(.text+0x1fc): undefined reference to `tee_client_open_context'

Change the CONFIG_NVMEM_STM32_ROMEM definition so it can only
be built-in if OPTEE is either built-in or disabled, and
make NVMEM_STM32_BSEC_OPTEE_TA a hidden symbol instead.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230206134356.839737-23-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>