MIPS: BMIPS: Enable CONFIG_SOC_BRCMSTB

Enable CONFIG_SOC_BRCMSTB in bmips_stb_defconfig. CONFIG_BRCMSTB_PM is
also enabled by default option in Kconfig.

Signed-off-by: Jaedon Shin <jaedon.shin@gmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Kevin Cernekee <cernekee@gmail.com>
Cc: linux-mips@linux-mips.org
Reviewed-by: James Hogan <jhogan@kernel.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/18590/


Signed-off-by: James Hogan <jhogan@kernel.org>