tools/automake: Revert "Do not use $(V) - force AM_V=1"

tools/automake: Revert "Do not use $(V) - force AM_V=1"

This reverts commit 43365ca66253 ("Do not use $(V) - force AM_V=1") as
it breaks verbose output in automake packages, deviating from the
upstream and expected behaviour.

As you can see, neither make command outputs the expected verbose
compile command lines:

```
$ make package/mtd-utils/{clean,compile} V=sc
...
  CCLD     lsmtd
  CC       nand-utils/nanddump.o
  CCLD     nanddump
...
```
```
$ make -C build_dir/target*/mtd-utils-2.1.1 clean
...
$ make -C build_dir/target*/mtd-utils-2.1.1 V=1
...
  CC       lib/libmtd.o
  CC       lib/libfec.o
  CC       lib/common.o
  CC       lib/libcrc32.o
```

The original reason for this commit was some packages failing to build
if V is set to something other than 0 or 1. See the discussion in PR
https://github.com/openwrt/openwrt/pull/2481 for how to fix this in the
package Makefile.

Ref: PR#2481
Acked-by: Mirko Vogt <mirko-openwrt@nanl.de>
Signed-off-by: Fredrik Olofsson <fredrik.olofsson@anyfinetworks.com>
[commit title/description facelift]
Signed-off-by: Petr Štetiar <ynezz@true.cz>