[binutils, ARM, 4/16] BF insns infrastructure with array of relocs in struct arm_it

This patch is part of a series of patches to add support for ARMv8.1-M Mainline
instructions to binutils.
This adds infrastructure for the Branch Future instructions (BF, BFX, BFL,
BFLX, BFCSEL).
These are the first instructions in ARM that have more than one relocations in
them. Their external relocations can be found in the 'ELF for the Arm
Architecture - ABI 2019Q1' document on developer.arm.com

This is the second infrastructure patch that adds support to allow up to
3 relocations in an instruction. This is done by changing the reloc member of
struct arm_it to an array instead (relocs[3]). All the previous occurrences of
reloc can now to referring to relocs[0].

ChangeLog entries are as follows :

*** gas/ChangeLog ***

2019-04-15  Sudakshina Das  <sudi.das@arm.com>

	* config/tc-arm.c (ARM_IT_MAX_RELOCS): New macro.
	(arm_it): Member reloc renamed relocs and updated to an array.
	Rest: Replace all occurrences of reloc to relocs[0].

gas/ChangeLog

@@ -1,3 +1,9 @@
+2019-04-15  Sudakshina Das  <sudi.das@arm.com>
+
+	* config/tc-arm.c (ARM_IT_MAX_RELOCS): New macro.
+	(arm_it): Member reloc renamed relocs and updated to an array.
+	Rest: Replace all occurrences of reloc to relocs[0].
+
 2019-04-15  Sudakshina Das  <sudi.das@arm.com>
 
 	* config/tc-arm.c (md_pcrel_from_section): New switch case