Make Marvell armv7 timer and wdt registers definitions common

Define timers registers for both SoCs and choose proper one during runtime
based on information from FDT.
In WDT driver there are different function for ArmadaXP and other ARMv5 SoCs.
In timer driver registers definitions are stored in resource_spec structure
and chosen during runtime.

Submitted by: Rafal Kozik <rk@semihalf.com>
Obtained from: Semihalf
Sponsored by: Stormshield
Differential Revision: https://reviews.freebsd.org/D14746