thermal: exynos: remove needless emul_time_shift abstraction

reg->emul_time_shift is used only in exynos_tmu_set_emulation()
and accessed only if TMU_SUPPORT_EMUL_TIME flag is set.  This
flag is not set for Exynos4210 and Exynos5440 (reg->emul_time_shift
field is not even assigned in exynos[4210,5440]_tmu_registers
and is assigned to identical value for all other SoC types) so
the abstraction is not needed and can be removed.

There should be no functional changes caused by this patch.

Cc: Amit Daniel Kachhap <amit.daniel@samsung.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Tested-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>