timer: bcmbca: use arm global timer for bcm63138 SoC

As STI timer is renamed to ARM A9 global timer, change BCM63138 to use
the new global timer config symbol name.

This patch applies on top of the my previous patch [1].

[1]: https://lists.denx.de/pipermail/u-boot/2022-August/491060.html



Signed-off-by: William Zhang <william.zhang@broadcom.com>