stand: Fix brand positioning on framebuffer console

The drawer.lua script ignores the values in loader_brand_x and
loader_brand_y on framebuffer consoles, always positioning the brand at
(1, 1).

Allow it to be positioned by accepting the x and y values just like the
text version. For example:

/boot/lua/gfx-nanobsd.lua:

return {
	brand = {
		graphic = {
			""
		},
		requires_color = true,
		image = "/boot/images/freebsd-logo-rev.png"
	}
}

/boot/loader.conf.d/bootloader.conf:

loader_logo="none"
loader_brand="nanobsd"
loader_brand_x="15"

PR: 255202
Reviewed by: manu, imp
Approved by: emaste (mentor)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D49092