watchdog/sb_watchdog: fix compilation problem due to COMPILE_TEST

Compiling sb_watchdog needs to clearly define SIBYTE_HDR_FEATURES.
In arch/mips/sibyte/Platform like:

  cflags-$(CONFIG_SIBYTE_BCM112X) +=                                      \
                -I$(srctree)/arch/mips/include/asm/mach-sibyte          \
                -DSIBYTE_HDR_FEATURES=SIBYTE_HDR_FMASK_1250_112x_ALL

Otherwise, SIBYTE_HDR_FEATURES is SIBYTE_HDR_FMASK_ALL.
SIBYTE_HDR_FMASK_ALL is mean:

 #define SIBYTE_HDR_FMASK_ALL  SIBYTE_HDR_FMASK_1250_ALL | SIBYTE_HDR_FMASK_112x_ALL \
				     | SIBYTE_HDR_FMASK_1480_ALL)

So, If not limited to CPU_SB1, we will get such an error:

  arch/mips/include/asm/sibyte/bcm1480_scd.h:261: error: "M_SPC_CFG_CLEAR" redefined [-Werror]
  arch/mips/include/asm/sibyte/bcm1480_scd.h:262: error: "M_SPC_CFG_ENABLE" redefined [-Werror]

Fixes: da2a68b3

 ("watchdog: Enable COMPILE_TEST where possible")
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>