video/vesa: drop "vesa-remap" command line option

If we get mode dimensions wrong, having the remapping size controllable
via command line option isn't going to help much. Drop the option.

While adjusting this also
- add __initdata to the variable,
- use ROUNDUP() instead of open-coding it.

Requested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

docs/misc/xen-command-line.pandoc

@@ -2489,9 +2489,6 @@ PCPUs when using the credit1 scheduler. This prevents rapid fluttering
 of a VCPU between CPUs, and reduces the implicit overheads such as
 cache-warming. 1ms (1000) has been measured as a good value.
 
-### vesa-map
-> `= <integer>`
-
 ### vesa-ram
 > `= <integer>`