pinctrl: renesas: r8a7778: Use physical addresses for PUPR regs

The handling of the LSI Pin Pull-Up Control Registers (PUPR) on R-Car
M1A uses register offsets instead of register physical addresses.
This is different from the handling on other R-Car parts.

Convert the bias handling from register offsets to physical addresses.
This increases uniformity, and prepares for consolidation of the bias
handling.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201028151637.1734130-7-geert+renesas@glider.be