staging: comedi: drivers: re-do PLX PCI 9080 LBRDx register values

Replace the existing macros in "plx9080.h" that define values for the
LBRD0 and LBRD1 registers.  Use the prefix `PLX_LBRD_` for macros that
apply to both registers, `PLX_LBRD0_` for macros that apply only to the
LBRD0 register, and `PLX_LBRD1_` for macros that apply only to the LBRD1
register.  Make use of the `BIT(x)` and `GENMASK(h,l)` macros to define
the values.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>