USB: EHCI: don't allocate hardware periodic table atomically by default

ehci_mem_init() is executed one time during ehci_init() and by default
all memory allocations but ehci->periodic are done not atomically,
GFP_KERNEL is passed as flags parameter.

Do similar allocation for ehci->periodic and free some space in
coherent atomic DMA pool by default.

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>