soc: xilinx: vcu: use bitfields for register definition

This makes the register accesses more readable and is closer to what is
usually used in the kernel.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/20210121071659.1226489-13-m.tretter@pengutronix.de


Signed-off-by: Stephen Boyd <sboyd@kernel.org>