tests/tcg: target/mips: Add tests for MSA pack instructions

Add tests for MSA pack instructions. This includes following
instructions:

  * PCKEV.B - pack even (bytes)
  * PCKEV.H - pack even (halfwords)
  * PCKEV.W - pack even (words)
  * PCKEV.D - pack even (doublewords)
  * PCKOD.B - pack odd (bytes)
  * PCKOD.H - pack odd (halfwords)
  * PCKOD.W - pack odd (words)
  * PCKOD.D - pack odd (doublewords)
  * VSHF.B - data preserving shuffle (bytes)
  * VSHF.H - data preserving shuffle (halfwords)
  * VSHF.W - data preserving shuffle (words)
  * VSHF.D - data preserving shuffle (doublewords)

Each test consists of 80 test cases, so altogether there are 960
test cases.

Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: Aleksandar Rikalo <arikalo@wavecomp.com>
Message-Id: <1551800076-8104-15-git-send-email-aleksandar.markovic@rt-rk.com>