lavapipe: report correct value for minMemoryMapAlignment
The vulkan spec says the following about vkMapMemory:
"ppData is a pointer to a void * variable in which is returned a host-accessible pointer to the beginning of the mapped range. This pointer minus offset must be aligned to at least VkPhysicalDeviceLimits::minMemoryMapAlignment."
So let's report the same value as the gallium-driver reports, otherwise we'll fail to adhere to the alignment requirement.
This fixes a few Piglit failures for Zink.
Closes: #4267 (closed)