ports: fomu: move more functions into ram for stability

The SPI flash on current Fomu firmware is slow.  Circuitpython runs
XIP from SPI flash, and so execution time can also be slow.  Ordinarily
this isn't a problem, however certain operations are time-sensitive.

In particular, USB function needs to be handled quickly in order to
prevent the host from re-enumerating the device.

Place several critical TinyUSB structures into RAM, as well as several
hot functions that are frequently called.  This reduces execution time
at the expense of system memory, and greatly improves system stability.

Signed-off-by: Sean Cross <sean@xobs.io>

ports/litex/boards/fomu/fomu-spi.ld

@@ -26,8 +26,42 @@ SECTIONS
         . = ALIGN(4);
         _sdata = .;        /* create a global symbol at data start; used by startup code in order to initialise the .data section in RAM */
 
-	*(.itcm.*)         /* Instruction Tightly Coupled Memory */
-	*(.dtcm_data.*)    /* Data Tightly Coupled Memory */
+        *(.itcm.*)         /* Instruction Tightly Coupled Memory */
+        *(.dtcm_data.*)    /* Data Tightly Coupled Memory */
+
+        *(.text.cmp_lfn)
+        *(.text.qstr_find_strn)
+        *(.text.dcd_edpt_xfer)
+        *(.text.pop_rule)
+        *(.text.ff_wtoupper)
+        *(.text.dir_find)
+        *(.text.push_rule)
+        *(.text.csr_writel)
+        *(.text.csr_readl)
+        *(.text.timer0_ev_pending_write)
+        *(.text.autoreload_tick)
+        *(.text.filesystem_tick)
+        *(.text.usb_background)
+
+        *(.text.dcd_*)
+        *(.text.tud_control_*)
+        *(.text.tud_cdc_n_write_flush)
+        *(.text.tud_task)
+        *(.text.tu_edpt_dir)
+        *(.text.tu_fifo_empty)
+        *(.text.usbd_edpt_busy)
+        *(.text.irq_getmask)
+        *(.text.irq_setmask)
+        *(.text.irq_pending)
+        *(.text._osal_q_lock)
+        *(.text.osal_queue_receive)
+
+        *(.text.mp_obj_get_type)
+        *(.text.mp_parse)
+        *(.text.parse_compile_execute)
+        *(.text.mp_map_lookup)
+        *(.text.mp_execute_bytecode) /* Note: this function is 7kb */
+
         *(.ramtext)        /* .text* sections (code) */
         *(.ramtext*)       /* .text* sections (code) */
         *(.data)           /* .data sections */
@@ -63,7 +97,7 @@ SECTIONS
         _sbss = .;         /* define a global symbol at bss start; used by startup code */
         *(.bss)
         *(.bss*)
-	*(.dtcm_bss.*)     /* Data Tightly Coupled Memory */
+        *(.dtcm_bss.*)     /* Data Tightly Coupled Memory */
         *(.sbss)
         *(.sbss*)
         *(COMMON)