riscv: kexec: Gate kexec image loader with CONFIG_CRASH_DUMP

[silvanshade]

This commit fixes the kernel build when CONFIG_CRASH_DUMP is not enabled. /cc @xingxg2022

[xingxg2022]

CONFIG_KEXEC_FILE depends on CONFIG_CRASH_DUMP. if you want to disable CONFIG_CRASH_DUMP, please also disable CONFIG_KEXEC_FILE.

[silvanshade]

CONFIG_KEXEC_FILE depends on CONFIG_CRASH_DUMP.

Are you sure this is the case? The definition of KEXEC_FILE does not seem to have a depends on CRASH_DUMP:

https://github.com/sophgo/linux-riscv/blob/93f987b13bc54332efd6f9cf95f4b62e2f7768eb/kernel/Kconfig.kexec#L38-L48

and:

https://github.com/sophgo/linux-riscv/blob/93f987b13bc54332efd6f9cf95f4b62e2f7768eb/kernel/Kconfig.kexec#L11-L12

Without this change, compiling without CONFIG_CRASH_DUMP will cause undeclared function errors.

[xingxg2022]

elf_kexec.c and image_kexec.c under arch/riscv/kernel directory both call some functions defined in kexec/crash_core.c. This is an implicit dependency and it is not reflected in Kconfig.

[silvanshade]

@xingxg2022 Why did you close it? I was planning to modify with your suggestion.