clk: meson: meson8b: Don't rely on u-boot to init all GP_PLL registers

Not all u-boot versions initialize the HHI_GP_PLL_CNTL[2-5] registers.
In that case all HHI_GPLL_PLL_CNTL[1-5] registers are 0x0 and when
booting Linux the PLL fails to lock.
The initialization sequence from u-boot is:
- put the PLL into reset
- write 0x59C88000 to HHI_GP_PLL_CNTL2
- write 0xCA463823 to HHI_GP_PLL_CNTL3
- write 0x0286A027 to HHI_GP_PLL_CNTL4
- write 0x00003000 to HHI_GP_PLL_CNTL5
- set M, N, OD and the enable bit
- take the PLL out of reset
- check if it has locked
- disable the PLL

In Linux we already initialize M, N, OD, the enable and the reset bits.
Also the HHI_GP_PLL_CNTL[2-5] registers with these magic values (the
exact meaning is unknown) so the PLL can lock when the vendor u-boot did
not initialize these registers yet.

Fixes: b882964b ("clk: meson: meson8b: add support for the GP_PLL clock on Meson8m2")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20200501215717.735393-1-martin.blumenstingl@googlemail.com