make brace placement in public header struct definitions consistent

placing the opening brace on the same line as the struct keyword/tag
is the style I prefer and seems to be the prevailing practice in more
recent additions.

these changes were generated by the command:

find include/ arch/*/bits -name '*.h' \
-exec sed -i '/^struct [^;{]*$/{N;s/\n/ /;}' {} +

and subsequently checked by hand to ensure that the regex did not pick
up any false positives.

arch/mips/bits/signal.h

@@ -17,8 +17,7 @@ typedef struct {
 		} fp_fregs[32];
 	} fp_r;
 } fpregset_t;
-struct sigcontext
-{
+struct sigcontext {
 	unsigned sc_regmask, sc_status;
 	unsigned long long sc_pc, sc_regs[32], sc_fpregs[32];
 	unsigned sc_ownedfp, sc_fpc_csr, sc_fpc_eir, sc_used_math, sc_dsp;