arch: Rename xxx_getsp to up_getsp

All modern desgin support stack pointer and it's also an
important information, so let's standardize this interface.

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

arch/x86/include/i486/arch.h

@@ -357,7 +357,7 @@ begin_packed_struct struct idt_ptr_s
 
 /* Return stack pointer */
 
-static inline uint32_t x86_getsp()
+static inline uint32_t up_getsp()
 {
   uint32_t regval;
 

arch/x86/include/tls.h

@@ -66,7 +66,7 @@
 static inline FAR struct tls_info_s *up_tls_info(void)
 {
   DEBUGASSERT(!up_interrupt_context());
-  return TLS_INFO((uintptr_t)x86_getsp());
+  return TLS_INFO((uintptr_t)up_getsp());
 }
 #else
 #  define up_tls_info() tls_get_info()