phy: spear1340-miphy: fix driver dependencies

ST SPEAR1340-MIPHY support should be available only on
ST SPEAr1340 machine.

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Pratyush Anand <pratyush.anand@st.com>
Cc: Mohit Kumar <mohit.kumar@st.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>