iommu/ipmmu-vmsa: Extract hardware context initialization

ipmmu_domain_init_context() takes care of (1) initializing the software
domain, and (2) initializing the hardware context for the domain.

Extract the code to initialize the hardware context into a new subroutine
ipmmu_domain_setup_context(), to prepare for later reuse.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>