ARM: shmobile: defconfig: Enable slab hardening and kmalloc buckets

Enable slab freelist metadata hardening, which in turn enables support
for allocation from separate kmalloc buckets.  The latter is recommended
to be enabled, as per its help text.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/96fc3f0ed509b6364d8aeb297d5acf4abed18404.1722349907.git.geert+renesas@glider.be

arch/arm/configs/shmobile_defconfig

@@ -24,6 +24,7 @@ CONFIG_CPUFREQ_DT=y
 CONFIG_VFP=y
 CONFIG_NEON=y
 # CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set
+CONFIG_SLAB_FREELIST_HARDENED=y
 CONFIG_CMA=y
 CONFIG_NET=y
 CONFIG_PACKET=y