PCI: rcar-host: Add OF Kconfig dependency to avoid objtool no-cfi warning

After commit 894af4a1cde6 ("objtool: Validate kCFI calls"), compile
testing pcie-rcar-host.c with CONFIG_FINEIBT=y and CONFIG_OF=n results
in a no-cfi objtool warning in rcar_pcie_probe():

$ cat allno.config
CONFIG_CFI=y
CONFIG_COMPILE_TEST=y
CONFIG_CPU_MITIGATIONS=y
CONFIG_GENERIC_PHY=y
CONFIG_MITIGATION_RETPOLINE=y
CONFIG_MODULES=y
CONFIG_PCI=y
CONFIG_PCI_MSI=y
CONFIG_PCIE_RCAR_HOST=y
CONFIG_X86_KERNEL_IBT=y

$ make -skj"$(nproc)" ARCH=x86_64 KCONFIG_ALLCONFIG=1 LLVM=1 clean allnoconfig vmlinux
vmlinux.o: warning: objtool: rcar_pcie_probe+0x191: no-cfi indirect call!

When CONFIG_OF is unset, of_device_get_match_data() returns NULL, so
LLVM knows this indirect call has no valid destination and drops the
kCFI setup before the call, triggering the objtool check that makes sure
all indirect calls have kCFI setup.

This driver depends on OF for probing with non-NULL data for every match
so this call will never be NULL in practice. Add a hard Kconfig
dependency on OF to avoid the warning.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202510092124.O2IX0Jek-lkp@intel.com/
Closes: https://github.com/ClangBuiltLinux/linux/issues/2134
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20251014-rcar_pcie_probe-avoid-nocfi-objtool-warning-v2-1-6e0204b002c6@kernel.org