mem: rename address mapping function to IOVA

mem: rename address mapping function to IOVA

The function rte_mem_virt2phy() is kept and used in functions which
works only with physical addresses.
For all other calls this function is replaced by rte_mem_virt2iova()
which does a direct mapping (no conversion) in the VA case.

Note: the new function rte_mem_virt2iova() function matches the
behaviour implemented in rte_mem_virt2phy() by the commit
680f6c12600f ("mem: honor IOVA mode in virt2phy")

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Santosh Shukla <santosh.shukla@caviumnetworks.com>