fix vector types in aarch64 register file structures

the ABI type for the vector registers in fpregset_t, struct
fpsimd_context, and struct user_fpsimd_struct is __uint128_t, which
was presumably originally not used because it's a nonstandard type,
but its existence is mandated by the aarch64 psABI. use of the wrong
type here broke software using these structures, and encouraged
incorrect fixes with casts rather than reinterpretation of
representation.

arch/aarch64/bits/signal.h

@@ -11,7 +11,7 @@ typedef unsigned long greg_t;
 typedef unsigned long gregset_t[34];
 
 typedef struct {
-	long double vregs[32];
+	__uint128_t vregs[32];
 	unsigned int fpsr;
 	unsigned int fpcr;
 } fpregset_t;
@@ -34,7 +34,7 @@ struct fpsimd_context {
 	struct _aarch64_ctx head;
 	unsigned int fpsr;
 	unsigned int fpcr;
-	long double vregs[32];
+	__uint128_t vregs[32];
 };
 struct esr_context {
 	struct _aarch64_ctx head;

arch/aarch64/bits/user.h

@@ -6,7 +6,7 @@ struct user_regs_struct {
 };
 
 struct user_fpsimd_struct {
-	long double vregs[32];
+	__uint128_t vregs[32];
 	unsigned int fpsr;
 	unsigned int fpcr;
 };