soc: intel_socfpga_std/cyclonev: enforce ARM_AARCH32_MMU

Currently the code in soc.c depends on the MMU of the CPU being enabled,
but this is not enforced. It is thus possible to cause a build error by
manually disabling it (as is required for some LLEXT tests, see #75289).

Make sure this is averted by explicitly selecting ARM_AARCH32_MMU in the
SoC Kconfig.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>