Default clock source for UARTs on Topcliff is external UART_CLK.
On CM-iTC USB_48MHz is used instead. After VCO2PLL and DIV
manipulations UARTs will receive 192 MHz.
Clock manipulations on Topcliff are controlled in pch_phub.c

v2: redone against the linux-next tree
v3: redone against linux/kernel/git/next/linux-next.git snapshot
Signed-off-by: NDenis Turischev <denis@compulab.co.il>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>