imx9: soc: Reuse and export low_drive_freq_update()

imx9: soc: Reuse and export low_drive_freq_update()

Reuse and export low_drive_freq_update() function. This way global imx9
board_fix_fdt() doesn't duplicate code. While low_drive_freq_update()
can be reused on boards such as phyCORE-i.MX93 (TARGET_PHYCORE_IMX93)
which is not using the global imx9 board_fix_fdt() implementation.

While at it, make printout logic less verbose by only outputting on the
error condition and not on each successful clock fixup. Also drop now
invalid comment (low_drive_freq_update() now does fixup for internal and
kernel device-tree).

Signed-off-by: Primoz Fiser <primoz.fiser@norik.com>