target/cortex_m,hla_target: rework Cortex-M register handling part 4

target/cortex_m,hla_target: rework Cortex-M register handling part 4

Consolidate low level register read/write.

Floating point registers were handled by target_read/write_u32
unlike other registers handled by cortexm_dap_read/write_coreregister_u32
There is no reason to do so in cortex_m.
Remove cortexm_dap_read/write_coreregister_u32
and use cortex_m_load/store_core_reg_u32 directly.

Similarly HLA adapters register read/write interface supports all registers
so use it for any floating point and other registers.

Change-Id: Ida679e5f4fec02d94ffb0bd3f265ed7ed2221cdc
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/5864
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>