soc/intel/pantherlake: Increase heap size for high-quality FW splash

This patch increases the default heap size from 1MB to 2MB (0x200000) to
accommodate rendering high-quality firmware splash BMP logos.

The previous 1MB heap size might be insufficient for larger, more
detailed OEM logos, potentially leading to memory exhaustion during the
splash screen display.

TEST=Able to render an OEM logo size ~512KB w/o any corruption.

Change-Id: I850247befc3904b6dc52e9872e8b99d53c2c9564
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/87265
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Reviewed-by: Jayvik Desai <jayvik@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/pantherlake/Kconfig

@@ -174,6 +174,10 @@ config FSP_TEMP_RAM_SIZE
 	  Refer to Platform FSP integration guide document to know
 	  the exact FSP requirement for Heap setup.
 
+config HEAP_SIZE
+	hex
+	default 0x200000
+
 config CHIPSET_DEVICETREE
 	string
 	default "soc/intel/pantherlake/chipset.cb"