payloads/iPXE: Fix PXE Kconfig question

As reported by Andrew Engelbrecht on the coreboot mailing list, there
was an issue when selecting the pxe rom file:

When using "make menuconfig", if "add pxe rom" is selected, then
the field below to set to the path of the pxe rom, the "add pxe rom"
option gets disabled.

This problem seems to be due to the use of the 'optional' Kconfig
keyword, so this section of the Kconfig is rewitten here to remove that
keyword and fix the issue.

Change-Id: I51680cb746160cb853c8679ac64e2d37989cb574
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/15555
Tested-by: build bot (Jenkins)
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
1 file changed