ARM: plt_size functions need to read instructions in right byte order

ARM: plt_size functions need to read instructions in right byte order

elf32_arm_plt0_size and elf32_arm_plt_size read instructions
to determine what is size of PLT entry.  However it does not
read instruction correctly in case of ARM big endian V7 case.
In this case instructions are still kept in little endian
order (BE8).

	* elf32-arm.c (read_code32): New function to read 32 bit
	arm instruction.
	(read_code16): New function to read 16 bit thumb instrution.
	(elf32_arm_plt0_size, elf32_arm_plt_size): Use read_code32
	and read_code16 to read instructions.