s390/mm: zero page cache synonyms for zEC12
s390/mm: zero page cache synonyms for zEC12

To avoid cache synonyms on System zEC12 32 independent zero pages are
required, one for each combination for bits 2**12 to 2**16 of the virtual
address. To avoid wasting too much memory on small virtual systems the
number of zero pages is limited to 4 if the memory size is less or equal
to 64MB.

Signed-off-by: Martin Schwidefsky <52616596d8f5df0d597e85ab515377f92f939c68@de.ibm.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs