nptl: Add default pthreadtypes-arch.h

nptl: Add default pthreadtypes-arch.h

This patch adds a default pthreadtypes-arch.h, the idea is to simpify
new ports inclusion and an override is required only if the architecture
adds some arch-specific extensions or requirement.

The default values on the new generic header are based on current
architecture define value and they are not optimal compared to current
code requirements as below.

  - On 64 bits __SIZEOF_PTHREAD_BARRIER_T is defined as 32 while is
    sizeof (struct pthread_barrier) is 20 bytes.

  - On 32 bits __SIZEOF_PTHREAD_ATTR_T is defined as 36 while
    sizeof (struct pthread_attr) is 32.

The default values are not changed so the generic header could be
used by some architectures.

Checked with a build on affected abis.

Change-Id: Ie0cd586258a2650f715c1af0c9fe4e7063b0409a