mx35: Clean up lowlevel_init

Clean up mx35 lowlevel_init:
 - Indent with tabs.
 - Fix comments.
 - Use defined values instead of literal constants.
 - Use defined macros instead of duplicating code.
 - Use macro parameters with default values instead of #define'd configs.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Stefano Babic <sbabic@denx.de>