memblock tests: add tests for memblock_trim_memory

Add tests for memblock_trim_memory() for the following scenarios:
- all regions aligned
- one unaligned region that is smaller than the alignment
- one unaligned region that is unaligned at the base
- one unaligned region that is unaligned at the end

Reviewed-by: Shaoqin Huang <shaoqin.huang@intel.com>
Signed-off-by: Rebecca Mckeever <remckee0@gmail.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Link: https://lore.kernel.org/r/0e5f55154a3b66581e04ba3717978795cbc08a5b.1661578349.git.remckee0@gmail.com