- Copy stable/10@296371 to releng/10.3 in preparation for 10.3-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.3.
- Update default pkg(8) configuration to use the quarterly branch.

Approved by: re (implicit)

MFC r262409, r267129, r267130, r280709:

Move the declaration for mpentry() into a header file

Fix broken SMP startup on Armada XP after r265694

Avoid using hard-coded SoC's register address in mptramp code for Armada XP

Use pmap_mapdev()/unmapdev() to temporarily map on-chip sram while copying
the startup trampoline code.

MFC 265694, 265705, 265784:

Move the mptramp code which is specific to the Marvell ArmadaXP SoC out of
the common locore.S file and into the mv/armadaxp directory.

Consolidate all the AP core startup stuff under a single #ifdef SMP block

Call idcache_inv_all from the AP core entry code before turning on the MMU.
Also, enable instruction and branch caches, which should be safe now that
they're properly initialized/invalidated first.

Move the mptramp code which is specific to the Marvell ArmadaXP SoC out of
the common locore.S file and into the mv/armadaxp directory.