Introduce initial support for Marvell Armada38x

Introduce initial support for Marvell Armada38x

This commit introduces initial support for Marvell Armada38x platform.
Changes:
- Add common DTS files for Armada38x SoCs and DTS file for A388-GP
- Add ARMADA38X kernel configuration
- Add option SOC_MV_ARMADA38X and set MV_PCI_PORTS
- Add list of files to compile
- Implement get_tclk(), get_sar_value(), cpu_reset() functions
- Add CPU ID and SoC numbers
- Correct ifdefs in arm/mv/timer.c

Reviewed by:    ian, imp
Obtained from:  Semihalf
Sponsored by:   Stormshield
Submitted by:   Michal Stanek <mst@semihalf.com>
Differential revision:  https://reviews.freebsd.org/D4210