clk: ti: dpll: add support for specifying max rate for DPLLs

DPLLs typically have a maximum rate they can support, and this varies
from DPLL to DPLL. Add support of the maximum rate value to the DPLL
data struct, and also add check for this in the DPLL round_rate function.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Nishanth Menon <nm@ti.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>