mips, uasm: Add workaround for Loongson-2F nop CPU errata

This patch implements a workaround for the Loongson-2F nop in generated,
code, if the existing option CONFIG_CPU_NOP_WORKAROUND is set. Before,
the binutils option -mfix-loongson2f-nop was enabled, but no workaround
was done when emitting MIPS code. Now, the nop pseudo instruction is
emitted as "or ax,ax,zero" instead of the default "sll zero,zero,0". This
is consistent with the workaround implemented by binutils.

Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Link: https://sourceware.org/legacy-ml/binutils/2009-11/msg00387.html
Link: https://lore.kernel.org/bpf/20211005165408.2305108-3-johan.almbladh@anyfinetworks.com

arch/mips/include/asm/uasm.h

@@ -249,7 +249,11 @@ static inline void uasm_l##lb(struct uasm_label **lab, u32 *addr)	\
 #define uasm_i_bnezl(buf, rs, off) uasm_i_bnel(buf, rs, 0, off)
 #define uasm_i_ehb(buf) uasm_i_sll(buf, 0, 0, 3)
 #define uasm_i_move(buf, a, b) UASM_i_ADDU(buf, a, 0, b)
+#ifdef CONFIG_CPU_NOP_WORKAROUNDS
+#define uasm_i_nop(buf) uasm_i_or(buf, 1, 1, 0)
+#else
 #define uasm_i_nop(buf) uasm_i_sll(buf, 0, 0, 0)
+#endif
 #define uasm_i_ssnop(buf) uasm_i_sll(buf, 0, 0, 1)
 
 static inline void uasm_i_drotr_safe(u32 **p, unsigned int a1,