phy: cadence: Sierra: Add array of input clocks in "struct cdns_sierra_phy"

Instead of having separate structure members for each input clock, add
an array for the input clocks within "struct cdns_sierra_phy". This is
in preparation for adding more input clocks required for supporting
additional clock combination.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>