riscv: drop the use of XIP_OFFSET in kernel_mapping_va_to_pa()

riscv: drop the use of XIP_OFFSET in kernel_mapping_va_to_pa()

XIP_OFFSET is the hard-coded offset of writable data section within the
kernel.

By hard-coding this value, the read-only section of the kernel (which is
placed before the writable data section) is restricted in size.

As a preparation to remove this hard-coded macro XIP_OFFSET entirely,
remove the use of XIP_OFFSET in kernel_mapping_va_to_pa(). The macro
XIP_OFFSET is used in this case to check if the virtual address is mapped
to Flash or to RAM. The same check can be done with kernel_map.xiprom_sz.

Signed-off-by: Nam Cao <namcao@linutronix.de>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/644c13d9467525a06f5d63d157875a35b2edb4bc.1717789719.git.namcao@linutronix.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>