xen/arm: p2m: Export p2m_*_lock helpers

xen/arm: p2m: Export p2m_*_lock helpers

Earlier patches exported the p2m interface (p2m_get_entry and
p2m_set_entry) to allow splitting xen/arch/arm/p2m.c. Those functions
require the callers to lock the p2m, so we need to export p2m_*_lock
helpers.

All helpers but p2m_write_unlock but p2m_write_unlock are moved in
xen/include/asm-arm/p2m.h to allow inlining. The helpers
p2m_write_unlock is kept in p2m.c because it depends on a static
function.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Tested-by: Tamas K Lengyel <tamas@tklengyel.com>