Allow arbitrary numbers of columns in the VNC server.

[grehan]

Summary

The prior code only allowed multiples of 32 for the
numbers of columns. Remove this restriction to allow
a forthcoming UEFI firmware update to allow arbitrary
x,y resolutions.

(the code for handling rows already supported values
that weren't multiples of 32)

Reviewed by Leon Dang, the original author.

Test Plan

The modified UEFI image at www.freebsd.org/~grehan/BHYVE_GOP_ares.fd
can be used to test this.

Tested with UEFI, Ubuntu live CDs, and FreeBSD with various
strange resolutions.