leds: LEDS_BLINK_LGM should depend on X86

The Intel Lightning Mountain (LGM) Serial Shift Output controller (SSO)
is only present on Intel Lightning Mountain SoCs.  Hence add a
dependency on X86, to prevent asking the user about this driver when
configuring a kernel without Intel Lightning Mountain platform support.

While at it, merge the other dependencies into a single statement.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Pavel Machek <pavel@ucw.cz>