Answer

"C1E Support" is a power saving function for CPU, you have to enable "C-state" first to be able to see this setting in BIOS.

Models

H110M PRO-VDL, H110M ECO, Z170A GAMING PRO CARBON, Z170A PC MATE, H110M PRO-VD PLUS , H110M PRO-VHL, Z170A GAMING M3, Z170A-S02, H170A GAMING PRO, Z170A KRAIT GAMING, Z170A GAMING PRO, Z170-A PRO, H110I PRO AC, Z170 KRAIT GAMING, H110M PRO-VDP, H110M PRO-VH PLUS, Z170I GAMING PRO AC, H110M GAMING, H110M PRO-VH, H110M GRENADE, Z170A-G45 GAMING, H170A PC MATE, H110M PRO-VDL D3, Z170A XPOWER GAMING TITANIUM EDITION, B150M MORTAR, Z170A SLI, Z170A SLI PLUS, Z170M MORTAR, H110M PRO-VD D3, Z170A GAMING M5, H110 PC MATE, B150M BAZOOKA PLUS, Z170A GAMING M9 ACK, B150 GAMING M3, H110I PRO, H170 GAMING M3, H110M-A PRO M2, B150A GAMING PRO, Z170A GAMING M7, H110M PRO-D, B150 PC MATE, H110M PRO-VD