ehci-hcd.c, musb_core, usb.h: Add USB_DMA_MINALIGN define for cache alignment

ehci-hcd.c, musb_core, usb.h: Add USB_DMA_MINALIGN define for cache alignment

The USB spec says that 32 bytes is the minimum required alignment.
However on some platforms we have a larger minimum requirement for cache
coherency.  In those cases, use that value rather than the USB spec
minimum.  We add a cpp check to <usb.h> to define USB_DMA_MINALIGN and
make use of it in ehci-hcd.c and musb_core.h.  We cannot use MAX() here
as we are not allowed to have tests inside of align(...).

Signed-off-by: Tom Rini <trini@ti.com>
[marek.vasut]: introduce some crazy macro voodoo
Signed-off-by: Marek Vasut <marex@denx.de>
[ilya.yanok]: moved external buffer fixes to separate patch,
we use {ALLOC,DEFINE}_ALIGN_BUFFER macros with alignment of USB_DMA_MINALIGN
for qh_list, qh and qtd structures to make sure they are proper aligned
for both controller and cache operations.
Signed-off-by: Ilya Yanok <ilya.yanok@cogentembedded.com>