xilinx: versal-net: Add support for timer and start it

xilinx: versal-net: Add support for timer and start it

Add support for starting timer by setting up time stamp generator
registers. This is done only for EL3 i.e. mini U-Boot case.
For other cases, it will be done TF-A.

Add COUNTER_FREQUENCY and IOU_SWITCH_DIVISOR0 to Kconfig so that they
can be tuned as required.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@amd.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/fcd8b0dc4b45a11f5e753afff42f84738ac813da.1673336645.git.michal.simek@amd.com