staging: dwc2: interpret all hwcfg and related register at init time

Before, the hwcfg registers were read at device init time, but
interpreted at various parts in the code. This commit unpacks the hwcfg
register values into a struct with properly labeled variables at init
time, which makes all the other code using these values more consise and
easier to read. Some values that were previously stored in the hsotg
struct are now moved into this new struct as well.

In addition to the hwcfg registers, the contents of some fifo size
registers are also unpacked. The hwcfg registers are read-only, so they
can be safely stored. The fifo size registers are read-write registers,
but their power-on values are significant: they give the maximum depth
of the fifo they describe.

This commit mostly moves code, but also attempts to simplify some
expressions from (val >> shift) & (mask >> shift) to
(val & mask) >> shift.

Finally, all of the parameters read from the hardware are debug printed
after unpacking them, so a bunch of debug prints can be removed from
other places.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>
Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>