Use PLATFORM for initializing Marvell ArmadaXP and Armada38X

Spliting armv5 and armv7 machdep is necessary for adding Armada38X and
ArmadaXP to GENERIC config.
PLATFORM framework checks SOC type in FDT and will select proper
initialization function implementation during runtime.
Pointers to SoC specific implementation are stored in array of
platform_method_t and provided to framework by FDT_PLATFORM_DEF macro.
PLATFORM framework supports also reset function. To simplify implementation
cpu_reset is moved from mv_common to armv5 and armv7 machdep.

Armada38X and ArmadaXP share now common list of files, so resolve all
dependencies as well.

Submitted by: Rafal Kozik <rk@semihalf.com>

	      Marcin Wojtas <mw@semihalf.com>

Reviewed by: mw
Obtained from: Semihalf
Sponsored by: Stormshield
Differential Revision: https://reviews.freebsd.org/D14744