[ARM] Refactor costs calculation for MEM.

[ARM] Refactor costs calculation for MEM.

This patch moves the calculation of costs for MEM into a
separate function, and reforms the calculation into two
parts. Firstly any additional cost of the addressing mode
is calculated, and then the cost of the memory access itself
is added.

In this patch, the calculation of the cost of the addressing
mode is omitted, to be added in a subsequent patch.

gcc/ChangeLog:

<date>  Charles Baylis  <charles.baylis@linaro.org>

        * config/arm/arm.c (arm_mem_costs): New function.
        (arm_rtx_costs_internal): Use arm_mem_costs.

gcc/testsuite/ChangeLog:

<date>  Charles Baylis  <charles.baylis@linaro.org>

        * gcc.target/arm/addr-modes-float.c: New test.
        * gcc.target/arm/addr-modes-int.c: New test.
        * gcc.target/arm/addr-modes.h: New header.

From-SVN: r255111