target/mips: Improve DSP R2/R3-related naming

target/mips: Improve DSP R2/R3-related naming

Do following replacements:

ASE_DSPR2 -> ASE_DSP_R2
ASE_DSPR3 -> ASE_DSP_R3
MIPS_HFLAG_DSPR2 -> MIPS_HFLAG_DSP_R2
MIPS_HFLAG_DSPR3 -> MIPS_HFLAG_DSP_R3
check_dspr2() -> check_dsp_r2()
check_dspr3() -> check_dsp_r3()

and several other similar minor replacements.

Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Stefan Markovic <smarkovic@wavecomp.com>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>