mmc: rtsx: add dump_reg_range to simplify dump register

Add a new function to dump register within a range.
We print 1 register a line before this patch,
this may make debug info too long when we add more register to dump.

The new dump_reg_range() dump to 8 register a line,
and it is easy to use.

Signed-off-by: Micky Ching <micky_ching@realsil.com.cn>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>