armv8: cache_v8: Fix pgtables setup when MMU is already enabled

When MMU is already enabled then dcache_enable() does not call mmu_setup()
and so setup_all_pgtables() is also never called.

In this situation when some driver calls mmu_set_region_dcache_behaviour()
function then U-Boot crashes with error message:

    Emergency page table not setup.

Fix this issue by explicitly calling setup_all_pgtables() in dcache_enable()
function near condition for mmu_setup().

This change fixes chainloading U-Boot from U-Boot on Turris Mox board which
uses mvneta ethernet driver which calls mmu_set_region_dcache_behaviour().

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>