ARM: tegra: misc cleanups triggered by Tegra124 review

ARM: tegra: misc cleanups triggered by Tegra124 review

Use a named constant for the PLL lock bit in enable_cpu_clocks().

Construct the complete value of pmc_pwrgate_toggle, rather than doing a
read-modify-write; the register is simple enough and doesn't need to
maintain state between operations.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>