In 1.1.0 RC6, it was called
MIN_Z_HEIGHT_FOR_HOMING
However, it appears in the latest, 1.1.0 RC7, they've changed it again to
// @section homing
#define Z_HOMING_HEIGHT 6 // (in mm) Minimal z height before homing (G28) for Z clearance above the bed, clamps, ...
// Be sure you have this distance over your Z_MAX_POS in case.