Link UEFI target documentation from target list

Author: sanxiyn

src/doc/rustc/src/platform-support.md

@@ -213,7 +213,7 @@ target | std | host | notes
 [`aarch64-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | ✓ |
 `aarch64-unknown-freebsd` | ✓ | ✓ | ARM64 FreeBSD
 `aarch64-unknown-hermit` | ✓ |  | ARM64 HermitCore
-`aarch64-unknown-uefi` | * |  | ARM64 UEFI
+[`aarch64-unknown-uefi`](platform-support/unknown-uefi.md) | * |  | ARM64 UEFI
 `aarch64-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (ILP32 ABI)
 `aarch64-unknown-netbsd` | ✓ | ✓ |
 [`aarch64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | ARM64 OpenBSD
@@ -250,7 +250,7 @@ target | std | host | notes
 `i686-unknown-haiku` | ✓ | ✓ | 32-bit Haiku
 `i686-unknown-netbsd` | ✓ | ✓ | NetBSD/i386 with SSE2
 [`i686-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 32-bit OpenBSD
-`i686-unknown-uefi` | * |  | 32-bit UEFI
+[`i686-unknown-uefi`](platform-support/unknown-uefi.md) | * |  | 32-bit UEFI
 `i686-uwp-windows-gnu` | ? |  |
 `i686-uwp-windows-msvc` | ? |  |
 `i686-wrs-vxworks` | ? |  |
@@ -307,7 +307,7 @@ target | std | host | notes
 `x86_64-unknown-l4re-uclibc` | ? |  |
 `x86_64-unknown-none-linuxkernel` | * |  | Linux kernel modules
 [`x86_64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 64-bit OpenBSD
-`x86_64-unknown-uefi` | * |  | 64-bit UEFI
+[`x86_64-unknown-uefi`](platform-support/unknown-uefi.md) | * |  | 64-bit UEFI
 `x86_64-uwp-windows-gnu` | ✓ |  |
 `x86_64-uwp-windows-msvc` | ✓ |  |
 `x86_64-wrs-vxworks` | ? |  |