arm64: mm: use IS_ENABLED(CONFIG_KEXEC_CORE) instead of #ifdef

Replace the conditional compilation using "#ifdef CONFIG_KEXEC_CORE" by a
check for "IS_ENABLED(CONFIG_KEXEC_CORE)", to simplify the code and
increase compile coverage.

Link: https://lkml.kernel.org/r/20211206160514.2000-5-jszhang@kernel.orgSigned-off-by: Jisheng Zhang <jszhang@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm64/mm/init.c

@@ -64,7 +64,6 @@ EXPORT_SYMBOL(memstart_addr);
  */
 phys_addr_t arm64_dma_phys_limit __ro_after_init;
 
-#ifdef CONFIG_KEXEC_CORE
 /*
  * reserve_crashkernel() - reserves memory for crash kernel
  *
@@ -78,6 +77,9 @@ static void __init reserve_crashkernel(void)
 	unsigned long long crash_max = arm64_dma_phys_limit;
 	int ret;
 
+	if (!IS_ENABLED(CONFIG_KEXEC_CORE))
+		return;
+
 	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
 				&crash_size, &crash_base);
 	/* no crashkernel= or invalid value specified */
@@ -110,11 +112,6 @@ static void __init reserve_crashkernel(void)
 	crashk_res.start = crash_base;
 	crashk_res.end = crash_base + crash_size - 1;
 }
-#else
-static void __init reserve_crashkernel(void)
-{
-}
-#endif /* CONFIG_KEXEC_CORE */
 
 /*
  * Return the maximum physical address for a zone accessible by the given bits