linux: remove kernel version checks for unsupported kernels

Following 2b06976 (#16479), anything gated on a kernel version before
4.18 can be always included/excluded.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed by: Brian Behlendorf <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: Tino Reichardt <[email protected]>
Signed-off-by: Rob Norris <[email protected]>
Closes #16545

Author: robn

include/os/linux/kernel/linux/simd_aarch64.h

@@ -56,17 +56,7 @@
 #include <asm/elf.h>
 #include <asm/hwcap.h>
 #include <linux/version.h>
-
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 17, 0)
 #include <asm/sysreg.h>
-#else
-#define	sys_reg(op0, op1, crn, crm, op2) ( \
-	((op0) << Op0_shift) | \
-	((op1) << Op1_shift) | \
-	((crn) << CRn_shift) | \
-	((crm) << CRm_shift) | \
-	((op2) << Op2_shift))
-#endif
 
 #define	ID_AA64PFR0_EL1		sys_reg(3, 0, 0, 1, 0)
 #define	ID_AA64ISAR0_EL1	sys_reg(3, 0, 0, 6, 0)

include/os/linux/kernel/linux/simd_powerpc.h

@@ -56,16 +56,10 @@
 #include <asm/switch_to.h>
 #include <sys/types.h>
 #include <linux/version.h>
-
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 7, 0)
 #include <asm/cpufeature.h>
-#else
-#include <asm/cputable.h>
-#endif
 
 #define	kfpu_allowed()			1
 
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 5, 0)
 #ifdef	CONFIG_ALTIVEC
 #define	ENABLE_KERNEL_ALTIVEC	enable_kernel_altivec();
 #define	DISABLE_KERNEL_ALTIVEC	disable_kernel_altivec();
@@ -101,11 +95,6 @@
 		DISABLE_KERNEL_ALTIVEC		\
 		preempt_enable();		\
 	}
-#else
-/* seems that before 4.5 no-one bothered */
-#define	kfpu_begin()
-#define	kfpu_end()		preempt_enable()
-#endif	/* Linux version >= 4.5 */
 
 #define	kfpu_init()		0
 #define	kfpu_fini()		((void) 0)

module/os/linux/spl/spl-proc.c

@@ -39,7 +39,7 @@
 #include <linux/version.h>
 #include "zfs_gitrev.h"
 
-#if defined(CONSTIFY_PLUGIN) && LINUX_VERSION_CODE >= KERNEL_VERSION(3, 8, 0)
+#if defined(CONSTIFY_PLUGIN)
 typedef struct ctl_table __no_const spl_ctl_table;
 #else
 typedef struct ctl_table spl_ctl_table;