Stdio for UEFI

- Uses Simple Text Output Protocol and Simple Text Input Protocol
- Reading is done one character at a time
- Writing is done with max 4096 characters

Signed-off-by: Ayush Singh <ayushdevel1325@gmail.com>

library/std/src/lib.rs

@@ -259,7 +259,7 @@
     all(target_vendor = "fortanix", target_env = "sgx"),
     feature(slice_index_methods, coerce_unsized, sgx_platform)
 )]
-#![cfg_attr(windows, feature(round_char_boundary))]
+#![cfg_attr(any(windows, target_os = "uefi"), feature(round_char_boundary))]
 #![cfg_attr(target_os = "xous", feature(slice_ptr_len))]
 //
 // Language features: