remoteproc: ti_k3_arm64: Program CNTFID0 register in GTC

ARMv8's generic timer[1] picks up it's graycode from GTC. However,
the frequency of the GTC is supposed to be programmed in CNTFID0[2]
register prior to enabling the GTC in CNTCR[3] register.

In K3 architecture, GTC provides a central time to many parts of the
SoC including graycode to the generic timer in the ARMv8 subsystem.
However, due to the central nature and the need to enable the counter
early in the boot process, the R5 based u-boot enables GTC and
programs it's frequency based on central needs of the system. This
may not be a constant 200MHz based on the system. The bootloader is
supposed to program the FID0 register with the correct frequency it
has sourced for GTC from the central system controller OR from PLLs
as appropriate, and TF-A is supposed[4] to use that as the frequency for
it's local timer.

Currently we are programming just the CNTCR[3] register to enable the
GTC, however we dont let TF-A know the frequency that GTC is actually
running at. A mismatch in programmed frequency and what we program for
generic timer will, as we can imagine, all kind of weird mayhem.

So, program the CNTFID0 register with the clock frequency. Note:
assigned-clock-rates should have set the clock frequency, so the only
operation we need to explicitly do is to retrieve the frequency and
program it in FID0 register.

Since the valid in K3 for GTC clock frequencies are < U32_MAX, we can
just cast the ulong and continue.

[1] https://developer.arm.com/documentation/100095/0002/generic-timer/generic-timer-register-summary/aarch64-generic-timer-register-summary
[2] https://developer.arm.com/docs/ddi0595/h/external-system-registers/cntfid0
[3] https://developer.arm.com/docs/ddi0595/h/external-system-registers/cntcr
[4] https://github.com/ARM-software/arm-trusted-firmware/commit/6a22d9ea3c7fa28d053d3ba264b49b7396a86f9e

Signed-off-by: Nishanth Menon <nm@ti.com>

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