.gitignore: drop include/asm/proc from ignore pattern

Commit 7d89982b stopped creating symbolic link
arch/${arch}/include/asm/proc.

arch/.gitignore should be updated.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Vasili Galka <vvv444@gmail.com>
diff --git a/arch/.gitignore b/arch/.gitignore
index a1fbe01..2714b86 100644
--- a/arch/.gitignore
+++ b/arch/.gitignore
@@ -1,2 +1 @@
 /*/include/asm/arch
-/*/include/asm/proc