On modern systems the regulator hierarchy can get quite long and nested
with regulators supplying other regulators. In some cases when debugging
it might be nice to get a tree of these regulators, their consumers
and the regulation constraints in one go.

To achieve this add a regulator_summary sysfs node, similar to
clk_summary in the common clock framework, that walks the regulator
list and creates a tree out of the regulators, their consumers and
core per-regulator settings.

On a rk3288-firefly the regulator_summary would for example look
something like:

 regulator                      use open bypass   value     min     max
-----------------------------------------------------------------------
 vcc_sys                          0   12      0  5000mV  5000mV  5000mV
    vcc_lan                       1    1      0  3300mV  3300mV  3300mV
       ff290000.ethernet                                    0mV     0mV
    vcca_33                       0    0      0  3300mV  3300mV  3300mV
    vcca_18                       0    0      0  1800mV  1800mV  1800mV
    vdd10_lcd                     0    0      0  1000mV  1000mV  1000mV
    vccio_sd                      0    0      0  3300mV  3300mV  3300mV
    vcc_20                        0    3      0  2000mV  2000mV  2000mV
       vcc18_lcd                  0    0      0  1800mV  1800mV  1800mV
       vcc_18                     0    2      0  1800mV  1800mV  1800mV
          ff100000.saradc                                   0mV     0mV
          ff0d0000.dwmmc                                 1650mV  1950mV
       vdd_10                     0    0      0  1000mV  1000mV  1000mV
    vdd_log                       0    0      0  1100mV  1100mV  1100mV
    vcc_io                        0    3      0  3300mV  3300mV  3300mV
       ff0f0000.dwmmc                                    3300mV  3400mV
       vcc_flash                  1    1      0  1800mV  1800mV  1800mV
          ff0f0000.dwmmc                                 1700mV  1950mV
       vcc_sd                     1    1      0  3300mV  3300mV  3300mV
          ff0c0000.dwmmc                                 3300mV  3400mV
    vcc_ddr                       0    0      0  1200mV  1200mV  1200mV
    vdd_gpu                       0    0      0  1000mV   850mV  1350mV
    vdd_cpu                       0    1      0   900mV   850mV  1350mV
       cpu0                                               900mV   900mV
    vcc_5v                        0    2      0  5000mV  5000mV  5000mV
       vcc_otg_5v                 0    0      0  5000mV  5000mV  5000mV
       vcc_host_5v                0    0      0  5000mV  5000mV  5000mV
 regulator-dummy                  0    0      0     0mV     0mV     0mV
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>
Signed-off-by: NMark Brown <broonie@kernel.org>