Update sys_write and sys_preload_store documentation to match implementation

Author: agren

libsyscall/sys_wrapper.c

@@ -47,8 +47,8 @@ int sys_dealloc(void)
 // Write data in `buf` to the app's flash area at byte `offset` within
 // the area.
 //
-// At most 4096 bytes can be written at once and `offset` must be a
-// multiple of 4096 bytes.
+// Up to storage area size bytes can be written at once and `offset` must be a
+// multiple of 256 bytes.
 //
 // Returns 0 on success.
 int sys_write(uint32_t offset, void *buf, size_t len)
@@ -97,8 +97,8 @@ int sys_preload_delete(void)
 // `sys_preload_store` many times as you receive the binary from the
 // client. Returns 0 on success.
 //
-// At most 4096 bytes can be written at once and `offset` must be a
-// multiple of 4096 bytes.
+// Up to preloaded app area size bytes can be written at once and `offset` must
+// be a multiple of 256 bytes.
 //
 // Only available for the verified management app.
 //