ARM: socfpga: Add clock entries into device tree

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: Dinh Nguyen <dinguyen@altera.com>
Reviewed-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Olof Johansson <olof@lixom.net>