clk: renesas: cpg-mssr: Add register pointers into struct cpg_mssr_priv

clk: renesas: cpg-mssr: Add register pointers into struct cpg_mssr_priv

To support other register layouts in the future, add register pointers
of {control,status,reset,reset_clear}_regs into struct cpg_mssr_priv.
After that, we can remove unused macros like MSTPSR().  No behavioral
changes.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/1599810232-29035-3-git-send-email-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>