PCI: ls-gen4: Make struct mobiveil_rp_ops constant

The struct mobiveil_rp_ops is not modified in this driver.

Thus, make this struct constant, which also moves data to a read-only
section decreasing object size and also improving overall security.

On a x86_64, with allmodconfig, as an example:

Before:
======
   text	   data	    bss	    dec	    hex	filename
   4446	    336	     32	   4814	   12ce	drivers/pci/controller/mobiveil/pcie-layerscape-gen4.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
   4454	    328	     32	   4814	   12ce	drivers/pci/controller/mobiveil/pcie-layerscape-gen4.o

[kwilczynski: commit log]
Link: https://lore.kernel.org/linux-pci/189fd881cc8fd80220e74e91820e12cf3a5be114.1719260294.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>