interconnect/wishbone: increase WB address width to 31

interconnect/wishbone: increase WB address width to 31

This is needed to support memory regions up to 4GB in size (currently
limited to 2GB, or 0x8000_0000).

FIXME: CI complains about assertions re. axi_lite.address_width in
       relationship to len(wishbone.adr) and wishbone_adr_shift, which
       seems to be a problem on the 32bit (vexriscv?) CPU used for CI,
       but seems to work fine on Rocket.

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
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