unicore32: pwm: Properly remap memory-mapped registers

Instead of writing to the timer controller registers by dereferencing a
pointer to the memory location, properly remap the memory region with a
call to ioremap_nocache() and access the registers using writel().

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Guan Xuetao <gxt@mprc.pku.edu.cn>
Tested-by: Qin Rui <qinrui@mprc.pku.edu.cn>