ARM: omap2plus_defconfig: drop unused POWER_AVS option

Commit 785b5bb4 ("PM: AVS: Drop the avs directory and the
corresponding Kconfig") moved AVS code to SOC-specific folders, and
removed corresponding Kconfig from drivers/power, leaving original
POWER_AVS config option enabled in omap2plus_defconfig file.

Remove the option, which has no references in the tree anymore.

Fixes: 785b5bb4 ("PM: AVS: Drop the avs directory and the corresponding Kconfig")
Signed-off-by: Andrey Zhizhikin <andrey.zhizhikin@leica-geosystems.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Nishanth Menon <nm@ti.com>
Cc: Nishanth Menon <nm@ti.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>