The call to BS->AllocatePages can cause the memory map to become framented, causing BS->GetMemoryMap to return EFI_BUFFER_TOO_SMALL more than once. For example this can happen on the MinnowBoard Turbot, causing the boot to stop with an error. Avoid this by calling GetMemoryMap in a loop. Reviewed by: imp, tsoome, kevans Differential Revision: https://reviews.freebsd.org/D19341