Add a variable and a macro to describe FP registers, assuming only D is
supported. FP code is conditional on CONFIG_FPU. The FP regs and FCSR
are copied separately to avoid copying struct padding. Tested by hand and
with the gdb testsuite.
Signed-off-by: Jim Wilson <jimw@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>