media: atomisp: get rid of an iomem abstraction layer

The hive_isp_css_custom_host_hrt.h code, together
with atomisp_helper.h, provides an abstraction layer for
some functions inside atomisp_compat_css20.c and atomisp_cmd.c.

There's no good reason for that. In a matter of fact, after
removing the abstraction, the code looked a lot cleaner
and easier to understand.

So, get rid of them.

While here, get rid also of the udelay(1) abstraction code.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>