In the bus_dma(9) framework, allocating a DMA buffer where maxsize is
smaller than the requested alignment (e.g. requesting a 64-byte
structure with 4096-byte page alignment) can trigger edge cases in
sub-page allocators and violates standard busdma conventions.
Round up maxsize, maxsegsize, and the loaded DMA buffer size to the
requested alignment boundary using roundup2(). This ensures that
page-aligned hardware structures consistently receive full-page
allocations across all architectures and releases, preventing alignment
failures during device resource configuration.
Signed-off-by: Jasper Tran O'Leary <jtranoleary@google.com>