clk: tegra: Set the clk parent of host1x to pll_p

The power-on default parent for this clock is pll_m, which turns out to
be wrong. Previously, bootloader reparented this clock.  We'll do it in
the kernel as well, so that there's one less thing that we depend on
bootloader to initialize.

Signed-off-by: Andrew Chew <achew@nvidia.com>
Signed-off-by: Mark Zhang <markz@nvidia.com>