memory: samsung: exynos5422-dmc: add missing and fix kerneldoc

Add missing kerneldoc to struct exynos5_dmc and correct the existing
kerneldoc in other places to fix W=1 warnings like:

    drivers/memory/samsung/exynos5422-dmc.c:107: warning: Function parameter or member 'freq_hz' not described in 'dmc_opp_table'
    drivers/memory/samsung/exynos5422-dmc.c:154: warning: Function parameter or member 'dev' not described in 'exynos5_dmc'
    drivers/memory/samsung/exynos5422-dmc.c:357: warning: Excess function parameter 'param' description in 'exynos5_set_bypass_dram_timings'
    drivers/memory/samsung/exynos5422-dmc.c:630: warning: Function parameter or member 'flags' not described in 'exynos5_dmc_get_volt_freq'
    drivers/memory/samsung/exynos5422-dmc.c:962: warning: cannot understand function prototype: 'struct devfreq_dev_profile exynos5_dmc_df_profile = '
    drivers/memory/samsung/exynos5422-dmc.c:1011: warning: Function parameter or member 'reg_timing_row' not described in 'create_timings_aligned'
    drivers/memory/samsung/exynos5422-dmc.c:1011: warning: Excess function parameter 'idx' description in 'create_timings_aligned'
    drivers/memory/samsung/exynos5422-dmc.c:1345: warning: Excess function parameter 'set' description in 'exynos5_dmc_set_pause_on_switching'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://lore.kernel.org/r/20200822163218.21857-3-krzk@kernel.org