ARM: SAMSUNG: Compile legacy IRQ and GPIO PM code only with ATAGS support

This patch adds new Kconfig symbols, SAMSUNG_PM_GPIO and S5P_IRQ_PM that
get enabled when GPIO_SAMSUNG, PM and S5P_PM are enabled, but only if
SAMSUNG_ATAGS is selected.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>