efi_loader: Make the pkcs7 header parsing function an extern

The pkcs7 header parsing functionality is pretty generic, and can be
used by other features like capsule authentication. Make the function
an extern, also changing it's name to efi_parse_pkcs7_header

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>

include/efi_loader.h

@@ -820,6 +820,10 @@ bool efi_secure_boot_enabled(void);
 bool efi_image_parse(void *efi, size_t len, struct efi_image_regions **regp,
 		     WIN_CERTIFICATE **auth, size_t *auth_len);
 
+struct pkcs7_message *efi_parse_pkcs7_header(const void *buf,
+					     size_t buflen,
+					     u8 **tmpbuf);
+
 /* runtime implementation of memcpy() */
 void efi_memcpy_runtime(void *dest, const void *src, size_t n);