powerpc: Use ALIGN instead of BLOCK

In the ld documentation under Builtin Functions:

  BLOCK(exp)

    This is a synonym for ALIGN, for compatibility with older linker scripts.

Clang's linker (lld) doesn't know about BLOCK so remove this use of
it.

Suggested-by: George Rimar <grimar@accesssoftek.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>