gdb/riscv: Add float status registers to save and restore reggroups

gdb/riscv: Add float status registers to save and restore reggroups

We should save and restore the floating point status registers.  This
became an issue when testing 32-bit float on a target with 64-bit with
the gdb.base/callfuncs.exp test.

gdb/ChangeLog:

	* riscv-tdep.c (riscv_register_reggroup_p): Save and restore fcsr,
	fflags, and frm registers.