Add IS_ALIGNED(x, a) macro helper

Change-Id: Ic5799e4bc03cabddece80cbc129b16f3a19ff9c5
rk27xx: sd: properly align buffer used for DMA transfers.

Commit 7d1a47cf ("Rewrite filesystem code (WIP)") exposed
bug in rk27xx sd driver. Buffer passed to sd_read/write_sectors()
doesn't has to be cacheline aligned. DMA transfers on
unaligned buffers is quiet dangerous thing.
Make sure that the buffer is aligned to cacheline size,
If not use a temporary aligned buffer for DMA transfer.

Change-Id: I91420f2b8d58159c80c3f15f4b35e88ea0dfd14c