mmu: Anonymous memory demand paging

Switch to demand paging for anonymous virtual memory.

  SPECjvm 2008 (higher is better)

  Baseline:

  Score on compiler.compiler: 347.06 ops/m
  Score on compiler.sunflow: 132.17 ops/m
  Score on compress: 107.59 ops/m
  Score on crypto.aes: 41.92 ops/m
  Score on crypto.rsa: 217.27 ops/m
  Score on crypto.signverify: 201.62 ops/m
  Score on derby: 184.81 ops/m
  Score on mpegaudio: 78.86 ops/m
  Score on scimark.fft.large: 35.91 ops/m
  Score on scimark.lu.large: 14.36 ops/m
  Score on scimark.sor.large: 26.16 ops/m
  Score on scimark.sparse.large: 37.64 ops/m
  Score on scimark.fft.small: 176.99 ops/m
  Score on scimark.lu.small: 222.76 ops/m
  Score on scimark.sor.small: 115.81 ops/m
  Score on scimark.sparse.small: 119.97 ops/m
  Score on scimark.monte_carlo: 141.17 ops/m
  Score on serial: 100.48 ops/m
  Score on sunflow: 79.54 ops/m
  Score on xml.transform: 217.30 ops/m
  Score on xml.validation: 349.88 ops/m

  Demand paging:

  Score on compiler.compiler: 338.57 ops/m
  Score on compiler.sunflow: 119.20 ops/m
  Score on compress: 120.18 ops/m
  Score on crypto.aes: 43.16 ops/m
  Score on crypto.rsa: 211.69 ops/m
  Score on crypto.signverify: 203.66 ops/m
  Score on derby: 181.10 ops/m
  Score on mpegaudio: 80.90 ops/m
  Score on scimark.fft.large: 34.15 ops/m
  Score on scimark.lu.large: 11.19 ops/m
  Score on scimark.sor.large: 22.99 ops/m
  Score on scimark.sparse.large: 36.62 ops/m
  Score on scimark.fft.small: 203.09 ops/m
  Score on scimark.lu.small: 236.72 ops/m
  Score on scimark.sor.small: 116.75 ops/m
  Score on scimark.sparse.small: 126.98 ops/m
  Score on scimark.monte_carlo: 152.86 ops/m
  Score on serial: 98.28 ops/m
  Score on sunflow: 78.93 ops/m
  Score on xml.transform: 216.34 ops/m
  Score on xml.validation: 381.52 ops/m

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
tst-mmap.so: mincore() tests for demand paging

As suggested by Nadav, add tests for mincore() interraction with demand
paging.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>