gdb:csky save fpu and vdsp info to struct csky_gdbarch_tdep

gdb:csky save fpu and vdsp info to struct csky_gdbarch_tdep

First, add three variables fpu_abi, fpu_hardfp and vdsp_version
to csky_gdbarch_tdep. They will be initialized from info.abfd in
cskg_gdbarch_init.

Now, they are just used to find a candidate among the list of pre-declared
architectures

Later, they will be used in gdbarch_return_value and gdbarch_push_dummy_call
for funtions described below:
fpu_abi: to check if the bfd is using VAL_CSKY_FPU_ABI_HARD or
VAL_CSKY_FPU_ABI_SOFT
fpu_hardfp: to check if the bfd is using VAL_CSKY_FPU_HARDFP_SINGLE
or VAL_CSKY_FPU_HARDFP_DOUBLE
vdsp_version: to check if a function is returned with CSKY_VRET_REGNUM