rockchip: rk3288: do not generate u-boot.rom anymore

rockchip: rk3288: do not generate u-boot.rom anymore

This was only used on RK3288 Chromebooks and the EVB.

If it follows the same pattern as for RK3399 Chromebooks where their
maintainer (Simon) agreed[1] to removal of u-boot.rom on the basis that
the generic u-boot-rockchip-spi.bin is now enough, let's do the same for
RK3288 and remove the last Rockchip users of u-boot.rom (and HAS_ROM
symbol).

At the same time, remove HAS_ROM symbol from the RK3288 Chromebooks and
EVB configs since they were used only for that.

SYS_SPI_U_BOOT_OFFS offset in rockchip-u-boot.dtsi for the u-boot-img
node of simple-bin-spi binman image matches the one used in u-boot.rom
except for the EVB.
The EVB doesn't have ROCKCHIP_SPI_IMAGE symbol enabled, so HAS_ROM had
no effect anyway. Even if it had, this would not have been enough
considering that SPL_SPI_LOAD symbol is not set, so U-Boot proper could
not be loaded from SPI even if SPL/TPL does.

Make sure u-boot-rockchip-spi.bin has the same size of u-boot.rom for
Chromebooks as that seems to be important.

[1] https://lore.kernel.org/u-boot/CAFLszTh-SewFod8dEOF3+e-wCE1qFF0CyxxR8CbQwy3BRW3k6w@mail.gmail.com/

Reviewed-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Tested-by: Simon Glass <sjg@chromium.org>  # chromebook-kevin
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>