riscv: Fix toolchain vector detection

A recent change to gcc flags rv64iv as no longer valid:

   cc1: sorry, unimplemented: Currently the 'V' implementation
   requires the 'M' extension

and as a result vector support is disabled. Fix this by adding m
to our toolchain vector detection code.
Signed-off-by: Anton Blanchard <antonb@tenstorrent.com>
Fixes: fa8e7cce ("riscv: Enable Vector code to be built")
Link: https://lore.kernel.org/r/20240819001131.1738806-1-antonb@tenstorrent.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/Kconfig

@@ -552,8 +552,8 @@ config RISCV_ISA_SVPBMT
 config TOOLCHAIN_HAS_V
 	bool
 	default y
-	depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64iv)
-	depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32iv)
+	depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64imv)
+	depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32imv)
 	depends on LLD_VERSION >= 140000 || LD_VERSION >= 23800
 	depends on AS_HAS_OPTION_ARCH