RISC-V: remove toolchain version checks for Zicbom

Commit b8c8687 ("riscv: fix detection of toolchain Zicbom
support") fixed building on systems where Zicbom was supported by the
compiler/assembler but not by the linker in an easily backportable
manner.
Now that the we have insn-defs for the 3 instructions, toolchain support
is no longer required for Zicbom.
Stop emitting "_zicbom" in -march when Zicbom is enabled & drop the
version checks entirely.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20230108163356.3063839-4-conor@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/Kconfig

@@ -416,16 +416,8 @@ config RISCV_ISA_SVPBMT
 
 	   If you don't know what to do here, say Y.
 
-config TOOLCHAIN_HAS_ZICBOM
-	bool
-	default y
-	depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zicbom)
-	depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zicbom)
-	depends on LLD_VERSION >= 150000 || LD_VERSION >= 23800
-
 config RISCV_ISA_ZICBOM
 	bool "Zicbom extension support for non-coherent DMA operation"
-	depends on TOOLCHAIN_HAS_ZICBOM
 	depends on !XIP_KERNEL && MMU
 	select RISCV_DMA_NONCOHERENT
 	select RISCV_ALTERNATIVE

arch/riscv/Makefile

@@ -58,9 +58,6 @@ riscv-march-$(CONFIG_RISCV_ISA_C)	:= $(riscv-march-y)c
 toolchain-need-zicsr-zifencei := $(call cc-option-yn, -march=$(riscv-march-y)_zicsr_zifencei)
 riscv-march-$(toolchain-need-zicsr-zifencei) := $(riscv-march-y)_zicsr_zifencei
 
-# Check if the toolchain supports Zicbom extension
-riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZICBOM) := $(riscv-march-y)_zicbom
-
 # Check if the toolchain supports Zihintpause extension
 riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZIHINTPAUSE) := $(riscv-march-y)_zihintpause