[nrf fromtree] tests: kernel: gen_isr_table: Fix kernel test for nRF FLPR target

Fix kernel `gen_isr_table` test for nRF FLPR target similairly
to PPR target.

Signed-off-by: Adam Kondraciuk <[email protected]>
(cherry picked from commit 85282d6)

Author: adamkondraciuk

tests/kernel/gen_isr_table/src/main.c

@@ -26,7 +26,7 @@ extern uint32_t _irq_vector_table[];
 #define ISR3_OFFSET	17
 #define ISR5_OFFSET	18
 #define TRIG_CHECK_SIZE	19
-#elif defined(CONFIG_SOC_NRF54H20_CPUPPR)
+#elif defined(CONFIG_SOC_NRF54H20_CPUPPR) || defined(CONFIG_SOC_NRF54H20_CPUFLPR)
 #define ISR1_OFFSET	14
 #define ISR3_OFFSET	15
 #define ISR5_OFFSET	16