arc: Fix alignment of the TLS Translation Control Block

The R_ARC_TLS_LE_32 is defined as S + A + TLS_TBSS - TLS_REL, where

  -  S is the base address of the symbol in the memory
  -  A is the symbol addendum
  -  TLS_TBSS is the TLS Translation Control Block size (aligned)
  -  TLS_REL is the base of the TLS section

Given the next code snip:

__thread int data_var = 12;
__attribute__((__aligned__(128))) __thread int data_var_128 = 128;
__thread int bss_var;
__attribute__((__aligned__(256))) __thread int bss_var_256;

int __start(void)
{
	return data_var + data_var_128 + bss_var + bss_var_256;
}

The current code returns different TLS_TBSS values for .tdata and
.tbss. This patch fixes this by using the linker provided tls_sec.

bfd/

	* elf32-arc.c (TLS_REL): Clean up.
	(TLS_TBSS): Use tls_sec alignment.
	(arc_do_relocation): Check if we have valid tls_sec.

Signed-off-by: Claudiu Zissulescu <claziss@gmail.com>