selftests/bpf: __imm_insn & __imm_const macro for bpf_misc.h

Add two convenience macro for BPF test cases,
allowing the following usage:

#include <linux/filter.h>

...
asm volatile (
...
".8byte %[raw_insn];"
...
"r1 += %[st_foo_offset];"
...
:
: __imm_insn(raw_insn, BPF_RAW_INSN(...)),
__imm_const(st_foo_offset, offsetof(struct st, foo))
: __clobber_all);

Signed-off-by: Eduard Zingerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/progs/bpf_misc.h

···
 #define __clobber_all "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "memory"
 #define __clobber_common "r0", "r1", "r2", "r3", "r4", "r5", "memory"
 #define __imm(name) [name]"i"(name)
+#define __imm_const(name, expr) [name]"i"(expr)
 #define __imm_addr(name) [name]"i"(&name)
 #define __imm_ptr(name) [name]"p"(&name)
+#define __imm_insn(name, expr) [name]"i"(*(long *)&(expr))
 
 #if defined(__TARGET_ARCH_x86)
 #define SYSCALL_WRAPPER 1