Adds the main PLL clock groups for SOCFPGA into device tree file
so that the clock framework to query the clock and clock rates
appropriately.

$cat /sys/kernel/debug/clk/clk_summary
   clock                        enable_cnt  prepare_cnt  rate
---------------------------------------------------------------------
 osc1                           2           2            25000000
    sdram_pll                   0           0            400000000
       s2f_usr2_clk             0           0            66666666
       ddr_dq_clk               0           0            200000000
       ddr_2x_dqs_clk           0           0            400000000
       ddr_dqs_clk              0           0            200000000
    periph_pll                  2           2            500000000
       s2f_usr1_clk             0           0            50000000
       per_base_clk             4           4            100000000
       per_nand_mmc_clk         0           0            25000000
       per_qsi_clk              0           0            250000000
       emac1_clk                1           1            125000000
       emac0_clk                0           0            125000000
    main_pll                    1           1            1600000000
       cfg_s2f_usr0_clk         0           0            100000000
       main_nand_sdmmc_clk      0           0            100000000
       main_qspi_clk            0           0            400000000
       dbg_base_clk             0           0            400000000
       mainclk                  0           0            400000000
       mpuclk                   1           1            800000000
          smp_twd               1           1            200000000
Signed-off-by: NDinh Nguyen <dinguyen@altera.com>
Reviewed-by: NPavel Machek <pavel@denx.de>
Signed-off-by: NOlof Johansson <olof@lixom.net>