arm: vmexit: add eoi test

Add a test to measure the EOI operation independently.  This should
probably be refined to EOI an actual interrupt which traps a maintenance
interrupt based on pinging the virtio testdev.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
arm: mmu: Squash warnings about unused vars

Some vars were left unused, squash the warnings about them by removing
them.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
arm: vmexit: Fix ipi test bug

Not setting ipi_ready can cause the SGI to be injected before it was
acked by the receiving CPU, which has no effect and renders the second
CPU to eventually never receiving the interrupt and the test program to
time out.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
arm: vmexit: Let individual tests to cycle reads

Since we changed the IPI test to wait until the IPI receiving CPU is
ready, there are cycles for each run of the test that should not be
counted in the overall test, therefore let the test implementation
itself do the measurements and return the value to the caller.  This
requires some mangling around, but the result is more flexible.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>