riscv: Move cast inside kernel_mapping_[pv]a_to_[vp]a

riscv: Move cast inside kernel_mapping_[pv]a_to_[vp]a

Before commit 44c922572952 ("RISC-V: enable XIP"), these macros cast
their argument to unsigned long. That commit moved the cast after an
assignment to an unsigned long variable, rendering it ineffectual.
Move the cast back, so we can remove the cast at each call site.

Reviewed-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Link: https://lore.kernel.org/r/20221126060920.65009-2-samuel@sholland.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>