x86: Merge sys_execve

Change 32-bit sys_execve to PTREGSCALL3, and merge with 64-bit.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
LKML-Reference: <1260403316-5679-4-git-send-email-brgerst@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>