There seems to be no LPCOpen library for the LPC804:
https://www.nxp.com/design/microcontrollers-developer-resources/lpcopen-libraries-and-examples/lpcopen-software-development-platform-lpc8xx:LPCOPEN-SOFTWARE-FOR-LPC8XX


Source: LPC804-EX-CODE-MCUXPRESSO.zip from nxp.com
available from here:
https://www.nxp.com/products/processors-and-microcontrollers/arm-microcontrollers/general-purpose-mcus/lpc800-cortex-m0-plus-/low-cost-microcontrollers-mcus-based-on-arm-cortex-m0-plus-core:LPC80X?tab=Design_Tools_Tab#t749
"LPC804 Example Code Bundle MCUXpresso"

 
 
Toplevel include should be "LPC8xx.h". 
The name "LPC8xx.h" might be misleading: This file is specific to the LPC804, but
I decided not to change the name, but keep the orginal file name from the above zip
folder. In  fact plan is not to modify any of the files in lpc_chip_804 so that they can 
be overwritten at any time with the original files (maybe chip_setup.h is an exception).

For some reason the variable "SystemCoreClock" is renamed to "main_clk".

While working in the code, I saw, that there are some issues in "lpc_chip_804":
 - Removed includes of "utilities.h" because the funcionality is not called
 - added inclusion of "swm.h" from "spi.h", because "spi.h" makes use of 
    some definitions from "swm.h"
 - Removed "Config_Syspll" declaration from "syscon.h" because it is removed in the src.
 - Alligned "unsigned int" with "uint32_t" declarations in syscon.h and .c 
 - Change the inclusion of "lpc8xx.h" to "LPC8xx.h" in i2c.h
 
 As a conclusion, I had to change the following files compared to the original zip content:
 i2c.h syscon.h syscon.c i2c.c spi.c spi.h plu.c