scripts: Do not strip .rela.dyn section

The .rela.dyn section contains runtime relocations and is only emitted
for a relocatable kernel.

riscv uses this section to relocate the kernel at runtime but that section
is stripped from vmlinux. That prevents kexec to successfully load vmlinux
since it does not contain the relocations info needed.

Fixes: 559d1e4 ("riscv: Use --emit-relocs in order to move .rela.dyn in init")
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250408072851.90275-1-alexghiti@rivosinc.com
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Author: Alexandre Ghiti

scripts/Makefile.vmlinux

@@ -13,7 +13,7 @@ ifdef CONFIG_ARCH_VMLINUX_NEEDS_RELOCS
 vmlinux-final := vmlinux.unstripped
 
 quiet_cmd_strip_relocs = RSTRIP  $@
-      cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel*' $< $@
+      cmd_strip_relocs = $(OBJCOPY) --remove-section='.rel*' --remove-section=!'.rel*.dyn' $< $@
 
 vmlinux: $(vmlinux-final) FORCE
 	$(call if_changed,strip_relocs)